Heart
Heart
Rock group
Heart is one of the few rock groups to feature women—Seattle-born sisters Ann and Nancy Wilson—as lead performers. The band has been working together, with some personnel changes, since the early 1970s, when the members were living in western Canada. Since their first album, Dreamboat Annie, went platinum in 1975, the entertainers in Heart have known every extreme that plagues famous rock bands, from the most dizzying heights of success to the most frustrating lulls in appeal.
As Gwenda Blair noted in Ms.magazine, however, the Wilson sisters “have always managed to hold up, whether they were facing … breakneck superstar tours, or… the seemingly endless uphill struggle to break out of… obscurity.” Blair attributed the group’s tenacity to the Wilsons’ special bond, “the easy camaraderie of best girlfriends mixed with the special familiarity and sensitivity of sisterhood.” The reporter added: “The continuity and companionship provided by that combination have carried the Wilsons a great distance over the years.”
For the Record…
Group formed in Seattle, Wash., in 1970; originally billed as White Heart; also performed briefly as Hocus-Pocus before adopting name Heart, 1970. Original band members iuncluded Anne Wilson (vocals), Nancy Wilson (guitar), Roger Fisher (guitar), Howard Leese (guitar), Michael Derosier (drums), and Steve Fossen (bass); have subsequently included more than twenty other members.
Addresses: Office— Suite 333, 219 First Ave. North, Seattle WA 98109.
Indeed, Heart has enjoyed an impressive level of success throughout most of its two-decade-long existence: four platinum albums, scores of sold-out tours, and number-one hits in the 1970s and 1980s. Blair described the group’s draw on its listeners: “Heart’s music, with its … bouncing-up-and-down-in-your-seat sound is what millions of people like. To some critics Heart’s sound may be sheer bubblegum blare fit only for undiscerning and voracious teen appetites. But to Ann and Nancy, escape and fantasy, not heavy messages or avant-garde music, is what rock is all about.”
Press coverage of Heart has centered on the Wilson sisters almost since the band began playing together in a one-room house in Vancouver. By all accounts, including their own, Ann and Nancy were ordinary, middle-class young women who grew up in Bellevue, a suburb of Seattle, Washington. They were teens in the 1960s, daughters of parents who embraced the radical causes and experimental lifestyles of that era. “We were pretty normal for the time we grew up in,” Ann told Rolling Stone.”What we experienced was going on in suburbs all over the country. We weren’t that different.” On the other hand, high school chum Sue Ennis, who has since written songs for Heart, recalled that the Wilsons were aloof from most of their peers, disdainful of the standard high school popularity contests, and happiest when they were alone in a bedroom, composing or listening to rock music. To quote Rolling Stone contributor Daisann McLane, as teenagers Ann and Nancy “played and wrote songs constantly, moody evocations of late-adolescent alienation.”
Ann graduated from Sammamish High School in 1968 with one ambition: to sing in a band. She began working with Tex Blaine and the Skyway Ranch Boys, but soon joined a psychedelic rock band called White Heart, staffed by guitarist Roger Fisher and bassist Steve Fossen. After doing a few gigs under the name Hocus-Pocus, the group members opted to call themselves Heart. Ann began a long romantic relationship with Michael Fisher, Roger’s brother, and Nancy eventually became involved with both the band (as a guitarist and flute player) and with Roger Fisher. Blair wrote of the Wilsons: “Two real-life Barbies, they … acquired their very own Kens—two handsome brothers who were also members of Heart.”
Heart’s early existence can hardly be described as a Barbie-and-Ken dream life. The band members moved to Vancouver and subsisted on brown rice and stolen fruit while trying to build a following. Laura Fissinger describes the group’s struggle, and ultimate success, in Rolling Stone: “In the early Seventies, Heart was just one more club band, doing six nights a week, four sets a night, and letter-perfect carbons of ‘Stairway to Heaven.’ Guitarist Howard Leese—the only other Heart member still around from the early days—was working for Mushroom records in Vancouver when he was tapped to produce the group’s first demo. Leese’s employers initially courted Ann as a solo act. When she said no, they took the whole passel.”
That “whole passel” turned out a debut album, Dreamboat Annie, that went platinum in seven months despite its obscure Canadian label and minimal promotion budget. The best known song from the album, a mysterious rocker called “Magic Man,” is today considered a classic. Heart turned out several more hit albums—Little Queen (1977), Magazine (1978), Dog and Butterfly (1978), and Bebe Le Strange (1980)—and had smash singles with “Crazy on You,” “Barracuda,” and “Dog and Butterfly.” McLane noted that the most successful Heart songs “graft heavy-metal musicianship to emotional, image-laden lyrics. This unlikely combination is held together by Ann’s powerful, three-octave soprano. She can belt and screech the hardest rock tune, then slide through every delicate nuance of a tender folk ballad.”
Nonstop touring also helped to promote Heart as a top rock band. The group’s dynamics—two sisters romantically involved with two brothers—made for frenzied press coverage and, at first, energetic live shows. Then problems began to beset Heart. First the group broke its contract with Mushroom and underwent a costly court battle over some unfinished tapes the label wanted to release. Then Ann ended her involvement with Mike Fisher, even though she credited him with the band’s success and suffered pangs of anxiety without his support. Nancy followed suit by breaking up with Roger Fisher and then firing him from the band. For a variety of reasons—the loss of Roger’s riveting concert presence among them—Heart went into a nosedive in the early 1980s.
The group continued to tour relentlessly, and continued to produce albums, but popular support faded. “Our management had us on the road nonstop,” Nancy told Rolling Stone.”We surfaced from our exhaustion just long enough to see that we were being mishandled and swept under the carpet.” Having taken responsibility for the direction of the band, the Wilsons switched from Epic to Capitol records in 1984. The following year—and on into 1986—Heart experienced a major comeback with their ninth album, Heart, and two top-selling singles, “What About Love” and “These Dreams.”
Ann and Nancy, whose titillating music videos have occasionally angered censorious critics, admit that their music is “wrong for any given time for what was in”—an observation echoed by some rock writers. The media may be condescending toward Heart’s “basic blueprint of heavy metal meets Joni Mitchell,” to quote Fissinger, but audiences respond to it warmly. According to Ariel Swartley in Rolling Stone, the members of Heart “need no showmanship to carry them: conviction has already been built into the melody, tension embedded in the harmonies.” Swartley also concluded that in Ann Wilson, Heart has “possibly the greatest female rock & roll singer ever…. And when she’s hot… the only reserved you’re thinking about is your seat for the next show.”
Selected discography
Dream boat Annie, Mushroom, 1976.
Little Queen, Portrait, 1977.
Magazine, Mushroom, 1978.
Dog and Butterfly, Portrait, 1978.
Bebe Le Strange, Epic, 1980.
Greatest Hits Live, Epic, 1980.
Private Audition, Epic, 1982.
Passionworks, Epic, 1983.
Heart, Capitol, 1985.
Bad Animals, Capitol, 1987.
Sources
High Fidelity, February, 1978.
Mademoiselle, June, 1982.
Rolling Stone, November 30, 1978; March 22, 1979; April 24, 1986.
—Anne Janette Johnson
Heart
HEART
HEART . Analysis of the symbolic values attached to the heart shows an unquestionable distance between the heart as a source of biological life and its diverse meanings for the emotional, moral, and religious life. The word heart may be specific, but the symbol is as multifarious as the polysemy of the term is rich. The range of meanings of heart is, indeed, at once based on a physiological reality (which entails a certain animistic conception of the individual) and on spiritual and mystical meditations—two sources that are intimately linked in most cultures.
It seems certain that the vitalistic conception of the heart as the seat of courage, strength, and life is represented by the presence in a great number of ancient societies of the custom of eating the heart of one's enemy to acquire his strength. Likewise, the notion of the heart as the source of life is the basis of the sacrifice usually practiced by the Aztec and earlier by the Maya. In the Inca empire, for instance, the heart was torn out, still beating, resulting in a copious hemorrhage. The flowing blood was nourishment for the Sun (symbolized by the eagle) and an invigorating drink for Tlaltecutli, the lord of the earth. The heart was considered the most precious part of the person; therefore it was the offering of life itself, a gift from the gods, that was achieved in the removal of a living heart and by the shedding of human blood.
The great symbolic themes relating to the heart were posed by the ancient Egyptians. It is the principal organ of physical life, and is well described in the medical papyri. It is also the center of emotional life, courage, and spiritual life. Thought, will, and wisdom reside there. The heart thus becomes the very locus of personality, capable of prayer to and love for the gods. But the heart is also man's memory, the witness to the deeds he accomplishes during his life. This is why, after death, hearts are weighed with Maat, the goddess of truth and justice, as a counterweight. The heart has a major role in the judgment of the dead, in which man's fidelity to moral prescriptions and social rules is examined. It is the dwelling place of Sia, the god of understanding, knowledge of the past, and creative imagination. If the dead person is "justified by his heart," if the judgment is in his favor, he then experiences union with the god: "Your heart is Re's heart," says the Book of Respiration (2.10), for in man's heart abides "the god who lives" in him, a kind of personal genius who determines the existence and the behavior of each individual. The heart is simultaneously soul, life, thought, witness of man's deeds, and the place where the god resides in order to guide man on this earth and to give an account in the afterlife of his actions. In the human heart, as necessary for life on earth as for survival after death, man may meet the divine.
According to the Egyptians, the gods also have a heart. The stela of King Shabaka, recapitulating an old theology of Memphis, shows that Ptah's heart is the seat of creative activity and the center of his imagination. All that was created by Ptah (the cosmic demiurge) was thought in his heart and came to life through the intermediary of his creating word.
The heart occupies an important place in the sacred texts of Hinduism, as well as in its techniques of spiritual meditation. The natural symbolism of the heart as the center of life and the psychological faculties appears in the Bṛhadāraṇyaka Upaniṣad (3.20–25). The heart is there described as the place where everything that exists takes shape: faith, supraintellectual knowledge, ontological truth, speech, and biological life (for "the sperm rests on the heart"). Even though the heart is hardly mentioned in the Vedas, which stress sacrificial ritual and praise of the divine, the outline of a "liturgy of the heart" can be seen in the oldest Upaniṣads. There it is conceived of as central in the activity of the ṛṣis, those seers who intuitively perceive the divine and express it in hymns. The heart is the secret place of their inspiration, where hymns are prepared to offer the gods, but it is also the critical authority that monitors the hymns' value. The heart thus becomes the place of divine vision, which is only given by grace to those who practice self-renunciation. It is understood that the heart's knowledge is satya, real and true, since it alone can enable one to pass from the unreal and the illusory to the real. Such knowledge is transformative, for it discovers, by means of the heart, the divine immanence within man. In bhakti, the heart is the seat of an aspiration to join the god and the center of a desire that "binds man at the level of his heart." Man should also reject the desire of natural and illusory realities in favor of the enjoyment of bliss and union with brahman. It is necessary to clear this heart by way of renunciation in order to become "a polished mirror" in which the god can be reflected. "When all the desires he carries in his heart have been cast away, then the mortal becomes immortal and from that time onward he delights in brahman ", says the Bṛhadāraṇyaka Upaniṣad (4.4.7).
The heart is thus the symbol of divine inhabitation in man. Four terms most often define this heart, citadel of the divine, of brahman: the grotto (Mahānārāyaṇa Upaniṣad 201, 469), the bird's nest (Haṃsa Upaniṣad 13), the ritual hearth, and especially the lotus, an ancient cosmogonic symbol on which the moralizing values of the pure and the impure, the emotional and the intellectual, are grafted (Dhyanabindu Upaniṣad 33–35 and 93). But what lives in this place? An impersonal, transcendent principle, the ātman (Chāndogya Upaniṣad 8.3.3), which exists and senses; the authority that perceives through the senses and that is the interior light in every human being; or else the image itself of the power of a personal god such as Śiva, Hari, Indra, the Everlasting, the Supreme (Mahānārāyaṇa Upaniṣad 269). The heart can thus become, by divine grace, the place for the vision of the god: "The man who is free from desire, all pain having vanished by grace of the creator, sees the Lord and his majesty" (Śvetāśvatara Upaniṣad 3.20). Thus the heart is the place of passage from duality to unity, from formlessness to form, from the unreal to the real (Chāndogya Upaniṣad 8.1.2–3; 8.3.1–2). The path of the heart, simultaneously one of meditation and renunciation, of the reversal of passions and desire for union, is thus the route from the carnal to the subtle, from the mortal to the immortal (Śvetāśvatara Upaniṣad 4.16.20).
The ancient Greek world had a rather undifferentiated psychological knowledge of the heart. In the writings of Homer, Hesiod, and the tragedians, kardia designates the place of the soul's life, the affects, the emotions, and the feelings. It is the place of secret thoughts and tactical intelligence. By a process of metonymy, the word stēthos (chest) is used in the sense of heart; thumos (the breath contained in the chest) designates the ardor that animates the feelings that lie in the heart and the thoughts that are formed there. It is this term, thumos, less concrete and more subtle, that predominates in the Classical age, but the philosophers introduced an important distinction. In agreement with doctors and certain philosophers like Empedocles (fifth century bce), who defined the heart as the seat of thought, the Epicureans and then the Stoics located intelligence there. Chrysippus asserted that the heart is the seat of dianoia, the source of language (Stoicorum vererum fragmenta 837, 838, 879). In response, Plato developed the theory of a tripartite soul: above the diaphragm is the mortal soul, the thumos that inspires good deeds; below are the passions, and the immortal principle of the soul is in the head. Therefore, only the ardor of generous deeds is found in the zone of the heart (Republic, book 4). Aristotle, however, situated sensations, sensory knowledge, memory, and imagination in the heart, but not the nous, or intelligence. Impossible to locate, the nous is not attached to any physical organ (Metaphysics 12.3.1070a). With Plotinus, all the metaphorical uses of kardia and thumos disappear in a distinct shift toward intellectualization, which will counterbalance any Judeo-Christian influence.
In the Bible, the word lev (heart) occurs 1,024 times, a frequency that testifies to the multivalence of a term common to the Hebrews and the ancient Semites, for whom the heart was an organ indispensable to life, the place for concentration of all the vital forces. If it beat more or less rapidly with respect to emotions felt, it was because, as the center of knowledge, it was an organ both receptive and active. The heart is the locus not only of the whole psychological and intellectual life but also of the moral life. It is man's interior, or qerev: "I shall put my law within them and write it on their hearts," says Yahveh (Jer. 31:33). This heart that permits understanding of divine things is, at first, recollection and remembrance of Yahveh's goodness. The expression "ascends to the heart" designates the necessary recollection: "From afar remember Yahveh and that Jerusalem ascends to your heart" (Jer. 51:50). The heart is therefore an active center where the ideas and impressions received are transformed into deeds; the heart thinks out man's projects and is the seat of the individual's creative power in the form of consciousness. Not only is the heart the center of moral life, but finally the center of religious life as well. It is the heart that experiences the fear of God and keeps faith to the alliance with Yahveh: the faithful heart belongs entirely to God, in whom it is fixed (1 Chr. 29:18).
During the Hellenistic age, when the Bible proliferated in the Greek translation, the word kardia, used to translate lev, was weighted with all the Semitic values of the heart and took on a new meaning to the extent that the association between heart, thought, and memory became commonplace. In the New Testament writings, a synthesis between Greek and biblical values of heart is achieved. The famous formula defining the ideal community of the first Christians "which has but one heart and one soul" (Acts 4:32) associates the new heart promised by Yahveh (Ez. 11:19) with a Greek proverb cited by Aristotle (Nicomachean Ethics 9.8.2) and used again by Cicero in order to define friendship (De amicitia 21.81). Heart is thus taken in its metaphorical sense in order to designate man's inner self, the place where his spiritual life is born and develops. But the third-century hellenization of an expression from the Christian faith makes more specific the use of heart, which loses its meaning of "understanding." Commenting on the beatitude of pure hearts (Mt. 5:8), Origen explains that to see God with the heart means to understand him with the spirit (De principiis 1.1.9). For Origen, the heart equals understanding; when the scripture says "heart," this is only a metaphor for emphasizing the "passage from the visible order to the invisible order." A similar Platonism will be developed later, more clearly, in the fourth century by Gregory of Nyssa, who explains the famous passage of the Song of Songs —"I sleep but my heart waketh" (5.2)—by bringing up the psuchē and the dianoia of the soul and of the intelligence in order to explain the word heart.
In the West, the term cor keeps the sense of the Hebrew lev, but Augustine enriches it with his psychological analyses in the Confessions. For him, the heart is the place of interiority and religious experience, which defines individuality: "My heart is where I am, such as I am" (Confessions 10.3.4). Little by little, however, in the Christian West the word heart becomes a simple metaphor for the whole emotional life, while in the East it keeps the meaning of spirit liberated from the passions and the affections and of the place for the understanding of divine things and the love of God.
A fundamental vein of Christian mysticism is that in which the divine heart and the human heart unite in an exchange of love. This mystical view of the heart, which appears in the West around the beginning of the eleventh century, is linked to a spirituality centered on the suffering humanity of Jesus Christ, as if devotion to the divine heart could not exist without an emotional reference to Jesus' heart of flesh and the shedding of his blood, which constitutes tangible proof of the love of a suffering and crucified God. In this heart of flesh, bared by the wound inflicted on the cross, the Christian mystics contemplated the same mystery of God's love, trying to specify its meaning in this heart, which had been pierced although it had already stopped beating. (Jn. 19:34). It was undoubtedly Anselm (1033–1109) who, meditating on the passion of Christ, was the first to glimpse this pierced heart as a revelation of God's love (Patrologia Latina 158.761–762).
The same idea is found in the writings of the Cistercian William of Saint-Thierry and of Bernard of Clairvaux (Patrologia Latina 183.1072). The emotionally pious individual ponders the wound in the divine heart and, confronted with its proof of God's love, wishes to penetrate it and lose himself in it. Such a desire for union, a desire to respond to God's love, has given rise to numerous mystical experiences: that of Lutgard of Aywières at the beginning of the thirteenth century, who was a "sympathetic" participant in the sufferings of the Passion and who "struck at the very heart of Jesus a tenderness so strong that she was forever strengthened"; or those mystical experiences of the cloistered nuns of Hefta in Saxony. Mechthild of Magdeburg (1207–1282) describes in detail how God put her own heart into his divine one burning with love, the two making but a single heart "as the water loses itself in the wine." God's heart is thus the place of sharing and joy while the mystic, like the apostle John, rests on the very breast of Jesus (Das fliessende Licht der Gottheit 2.38).
From this monastery in Hefta, where other nuns shared the devotion to Jesus' heart shown by Saint Gertrude (1256–1334), the custom passed to the Franciscans. The memory of their founder's stigmata and their popular emotional preaching developed a piety founded on the contemplation of the afflictions of the crucified one and his wounded heart. In his Vitis mystica, Bonaventure (1221–1274) praises "the good Jesus' heart" and stresses the love, revealed by Christ in his incarnation, that is sensitive to human nature. This wounded heart is the vital and tangible expression of God's blessings. But it is also the place into which the human soul must penetrate "as if into a promised land where he will find sweetness, purity, and even God's love," says Ubertino da Casale (Arbor vitae crucifixae Jesu, c. 1320). This desire for union with Jesus' heart is so great that, through many repetitions in the course of these unifying experiences, an exchange of hearts between Christ and the mystic is effected, as in the cases of Lutgard, Catherine of Siena, Dorothy of Montau, and, later, Marguerite-Marie Alacoque. It is a symbolic exchange, of course, in which God's will is voluntarily substituted by a human being for his or her own and which is the sign of a transforming union born of that "new spirit and that new heart" prophesied by Ezekiel (36:26–27). This symbol of Christ's heart replacing that of the mystic represents "the union of the uncreated spirit and the created spirit that is realized by the preeminence of grace," explains Thomas of Cantimpré in the Life of Lutgard (Acta sanctorum, June, vol. 4, p. 193). The heart is the whole human being, who always wishes to unite more fully with the person of the word incarnate himself perceived in a heart, which is the sign of his love and the center "where all the virtue of divinity is enclosed."
In the Christian East, the "prayer of the heart," from the time of the Desert Fathers to our own time, has combined an ancient technique of breath control with the invocation of Jesus' name, in order to "make the spirit descend into the heart." By concentrating his gaze on the interior of his heart, one discovers it as the locus of emotional life, desires, and love. Then one must melt one's perceptual and intellectual thoughts there, as if in a brazier, and let them heat up and burn until a cry breaks out in one's heart, a call to Jesus, the unique source of that love. The heart is thus the space where the body and soul penetrate each other and coexist, just as the inhaled air mixes with the very breath of life. The discovery of the heart therefore reestablishes human nature in its original state, before the Fall, in rediscovering the energy of the Holy Spirit given by baptism, and in becoming the temple of God once again. The expression "prayer of the heart" is therefore metonymical, although the method of prayer described appears to link it to a specific respiratory technique. Hesychast spirituality insists on the necessity of ascesis to purify the heart of man, who may then come back to the reason why he was created and discover truth. Man then receives illumination from the sun of justice, whose light shines in his heart, which thus becomes the place where God reveals himself and the place of God's desire, where the created being lets the Lord live, and finally knows hēsuchia: the eternal joy of being united with him forever (Mt. 17:4).
Exactly this conception of the heart as the place of God's desire and the organ of prayer and knowledge of divine things is found again in Pascal in seventeenth-century France, where the devotion to the Sacred Heart of Jesus proliferated, with such devotees as Marie des Vallées, Jean Eudes, and Marguerite-Marie Alacoque. Indeed, the Pascalian heart is the center of neither the emotions nor the faculties of the soul; it is the place of resolution and adherence. It is will, and through it the individual is defined and expressed. But it is, in addition, the organ that knows an order superior to that of reason: "It is the heart that feels God and not reason: this is what faith is, God susceptible to the heart and not to reason" (Pensées 278). Pascal meant that reason is not useless, but that it remains insufficient, for it belongs to the natural order, whereas "the heart has reasons that reason knows not" (ibid., 277). The knowledge of God is not an abstract thought; it emerges from the very existence of man, and it resides in the desire for abundance: "My whole heart reaches out to know where the true good is in order to follow it." For, as Pascal wrote in 1658 in his Art of Persuasion, "man discovers the truth of which he speaks inside himself." Thus, in diverse cultures and religious traditions, the heart has the profound value of symbolizing and structuring all of human life, the spiritual as much as the physical.
Bibliography
Ancelet-Hustache, Jeanne. Mechtilde de Magdebourg, 1207–1872: Étude de psychologie religieuse. Paris, 1926.
Claudel, Paul, et al. Le cœur. Bruges, 1950. A volume in the series "Études carmélitaines."
Meyendorff, John. A Study of Gregory Palamas. London, 1964.
Onians, Richard B. The Origins of European Thought. Cambridge, U.K., 1954.
Varenne, Jean, trans. and ed. Upanishads du Yoga. Paris, 1971.
Michel Meslin (1987)
Translated from French by Kristine Anderson
Heart
Heart
A heart is a means to circulate blood through the body of an animal . Among the lower species such as insects , arachnids , and others, the heart may simply be an expanded area in a blood vessel and may occur a number of times. The earthworm, for example, has 10 such "hearts." These areas contract rhythmically to force the blood through the aorta, or blood vessel.
Not until the evolution of the higher vertebrates does the heart achieve its ultimate form, that of a chambered organ with differentiated purposes. Even the lower chordates , such as amphioxus, possess hearts not more advanced than those in the earthworm. It is simply a pulsating blood vessel that moves blood through the body.
Blood
In a complex organism such as a vertebrate, with multiple cell layers and complex organ systems, blood serves to distribute nourishment and oxygen to the cells and remove waste products. Specialized cells within the blood, such as the red blood cells (erythrocytes) and white blood cells (leukocytes) serve specialized functions. The red cells hold and distribute oxygen to release in the cells and return carbon dioxide to the lungs to be eliminated. The white cells carry out immune functions to destroy invading bacteria and other foreign material. Still other components of the blood are involved in forming clots when a blood vessel is opened. The liquid medium, the plasma , carries vitamins and other nutrients throughout the body.
Animals require a means for the blood to obtain oxygen, whether through gills or lungs, and a means to propel the blood through those structures. The heart is central to that purpose.
The multiform heart
The heart is a pulsating organ that pushes a liquid medium throughout the body. It may be as simple as one chamber or as complex as four chambers, as in the higher mammals . In all animals, however, it is an organ that must function day after day without pause to keep the blood moving.
In general, blood that returns from the body or from the oxygen exchanging structures returns to an atrium, which is simply a holding chamber. The atrium (plural is atria) empties into another chamber called the ventricle, a muscular chamber that contracts rhythmically to propel the blood through the body. Movement of the blood between chambers and in and out of the heart is controlled by valves that allow movement only in one direction.
The lower vertebrates such as the hagfish and other fish have two-chambered hearts. The ventricle pumps blood forward through the gills to obtain oxygen and dispose of carbon dioxide. From there the blood enters the dorsal aorta and is carried through the body. The blood returns to the heart by means of the sinus venosus, which empties into the auricle or atrium. From there it is passed into the ventricle and the cycle begins again.
Terrestrial vertebrates such as amphibians , have three-chambered hearts and a more complex circulatory system . The third chamber is another auricle or atrium. Unoxygenated blood from the body of the animal returns to the right auricle and the oxygenated blood from the lungs goes into the left auricle. Both auricles contract simultaneously and empty their contents into the single ventricle. The oxygenated and unoxygenated blood does not mix to any degree because of specialized muscle strands in the ventricle. Also, the ventricle contracts immediately after the auricles so the bloods do not have time to mix. When the ventricle contracts, the unoxygenated blood is forced from the heart first and enters the pulmocutaneous vessels leading to the lungs and skin for oxygen exchange. The oxygenated blood enters the truncus arteriosus and flows to the head, arms, body, and hind legs.
Reptiles demonstrate a further step in heart development—a divided ventricle. The wall in the ventricle dividing left from right is incomplete except in crocodiles and alligators. Blood from the body enters the right auricle from which it passes into the right side of the ventricle and is pumped through the lungs. Oxygenated blood from the lungs enters the left auricle and passes into the left side of the ventricle. From there it moves out through the two aortic arches to the body.
Among the crocodilia, however, a peculiar structure of the aortae allows mixing of arterial and venous blood. The left aortic arch rises from the right side of the heart, as does the pulmonary artery. Thus, unoxygenated blood pumped from the right ventricle goes to the lungs through the pulmonary artery and also into the aortic arch and out into the body where it will mix with oxygenated blood. The right aortic arch rises from the left ventricle and carries only oxygenated blood.
Birds also possess four-chambered hearts, in this case with complete separation of the two ventricles. They have only one aortic arch, however, and that is the right arch.
Mammals, including humans, also have a four-chambered heart, but the aortic arch curves up and to the left as it leaves the heart. Here, as with birds, there is no mixing of venous and arterial blood under normal circumstances. Though the heart appears to be a simple organ, it requires a complex series of nerve stimulations, valve openings, and muscle contractions to adequately achieve its purpose.
The human heart
Located in the thoracic cavity, the heart is a four-chambered muscular organ that serves as the primary pump or driving force within the circulatory system. The heart contains a special form of muscle, appropriately named cardiac muscle, that has intrinsic contractility (i.e., is able to beat on its own, without nervous system control).
The Chinese were aware more than 2,000 years ago that the heart is a pump that forces blood through a maze of arteries . The Greeks, however, believed the blood did
not circulate at all, and their ideas dominated medical science until the seventeenth century. The Greek physician Galen published a great deal on the human body and its functions, much of which was incorrect, but his doctrines held sway for hundreds of years. Not until the 1600s did William Harvey, through human and animal experiments, discover that the heart circulates the blood. He published his findings in 1628, thus bringing Western medical science in line with that of the ancient Chinese.
The human heart on the average weighs about 10.5 oz (300 g). It is a four-chambered, cone-shaped organ about the size of a closed fist that lies in the mid-thorax, under the breastbone (sternum). Nestled between the lungs, the heart is covered by a fibrous sac called the pericardium. This important organ is protected within a bony cage formed by the ribs, sternum, and spine.
In its ceaseless work, the heart contracts some 100,000 times a day to drive blood through about 60,000 mi (96,000 km) of vessels to nourish each of the trillions of cells in the body. Each contraction of the ventricles forces about 2.5 oz (0.075 l) of blood into the circulation, which adds up to about 10 pt (4.7 l) of blood every minute. On average, the heart will pump about 2,500 gal (9,475 l) of blood in a day, and that may go up to as much as 5,000 gal (18,950 l) with exertion. In a lifetime the heart will pump about 100 million gal of blood.
The chambers of the human heart are divided into two upper (superior) atrial chambers and two thickerwalled, heavily muscular inferior ventricular chambers. The right and left sides of the heart are divided by a thick septum. The right side of the heart is on the same side of the heart as is the right arm of the patient. The atrial and ventricular chambers on each side of the septum constitute separate collection and pumping systems for the pulmonary (right side) and systemic circulation (left side). The coronary sulcus or grove separates the atria from the ventricles. The left and right side atrial and ventricular chambers each are separated by a series of one way valves that, when properly functioning, allow blood to move in one direction, but prohibit it from regurgitating (flowing back through the valve).
Deoxygenated blood—returned to the heart from the systemic circulatory venous system—enters the right atrium of the heart through the superior and inferior vena cava. Auricles lie on each atrium and are most visible when the atria are drained and deflated. The auricles (so named because they resembled ear flaps) allow for greater atrial expansion. Pectinate muscles on the auricles assist with atrial contraction. Small contractions within the right atrium, and pressure differences caused by evacuation of blood in the lower (inferior) right ventricle, cause this deoxygenated blood to move through the tricuspid valve during diastole (the portion of the heart's contractile cycle between contractions, and a period of lower pressure as compared to systole) into the right ventricle. When the heart contracts, a sweeping wave of pressure forces open the pulmonic semilunar valve that allows blood to rush from the right ventricle into the pulmonary artery where it is travels to the lungs for oxygenation and other gaseous exchanges.
Freshly oxygenated blood returns to the heart from the pulmonary circulation through the pulmonary vein the empties into the left atrium. During diastole, the oxygenated blood moves from the left atrium into the left ventricle through the mitral valve. During systolic contraction, the oxygenated blood is pumped under high pressure through the semilunar aortic valve into the aorta and thus, enters the systemic circulatory system.
As the volume and pressure rise during the filling of the right and left ventricles, the increased pressure snaps shut the flaps of the atrioventricular valves (tricuspid and mitral valves) anchored by fibrous connection to the left and right ventricles. The pressure in the ventricles seals the valves and as the pressure increases during systole, the valves seal becomes further compressed. A prolapse in one of the valves (a pushing through of one of the cusps) leads to blood flow back through the valve. The cusps are held against prolapse by the chordae tendineae, thin cords that attach the cusps to papillary muscles.
The heart and great vessels attached to it are encased within a multi-layered pericardium. The outer layer is fibrous and covers a double membraned inner sac-like structure termed the pericardial cavity that is filled with pericardial fluid. The pericardial fluid acts to reduce friction between the heart, the pericardial membranes, and the thoracic wall as the heart contracts and expands during the cardiac cycle .
The heart muscle is composed of three distinct layers. The outermost layer, the outer epicardium, is separated from the inner endocardium by the middle pericardium. The outer epicardium is continuous and in some places the same as the visceral pericardium. Epicardium protects the heart and is invested with capillaries , nerves, and lymph vessels. The middle myocardium is a think layer of cardiac muscle. The innermost endocardium contains connective tissue and Purkinje fibers. The endocardium is continuous with the lining of the great vessels attached to the heart and it lines all valve and cardiac inner surfaces.
Heart muscle does not directly take up oxygen from the blood it pumps. A specialized set of vessels (e.g., the left and right coronary arteries and their branches) supply oxygenated blood to the heart muscle and constitute the coronary circulation. A heart attack occurs whenever blood flow is occluded (blocked).
The fossa ovalis is a remnant or the embryonic foramen ovale that allows blood to flow between the left and right atria in the developing fetus.
Regulation of the heart
Various intrinsic, neural, and hormonal factors act to influence the rhythm control and impulse conduction within the heart. The rhythmic control of the cardiac cycle and its accompanying heartbeat relies on the regulation of impulses generated and conducted within the heart. Regulation of the cardiac cycle is also achieved via the autonomic nervous system. The sympathetic and parasympathetic divisions of the autonomic system regulate heart rhythm by affecting the same intrinsic impulse conducting mechanisms that lie within the heart in opposing ways.
Cardiac muscle is self-contractile because it is capable of generating a spontaneous electrochemical signal as it contracts. This signal induces surrounding cardiac muscle tissue to contract and a wave-like contraction of the heart can result from the initial contraction of a few localized cardiac cells.
The cardiac cycle describes the normal rhythmic series of cardiac muscular contractions. The cardiac cycle can be subdivided into the systolic and diastolic phases. Systole occurs when the ventricles of the heart contract and diastole occurs between ventricular contractions when the right and left ventricles relax and fill. The sinoatrial node (S-A node) and atrioventricular node (AV node) of the heart act as pacemakers of the cardiac cycle.
The contractile systolic phase begins with a localized contraction of specialized cardiac muscle fibers within the sino-atrial node. The S-A node is composed of nodal tissue that contains a mixture of muscle and neural cell properties. The contraction of these fibers generates an electrical signal that then propagates throughout the surrounding cardiac muscle tissue. In a contractile wave originating at the S-A node, the right atrium muscle contracts (forcing blood into the right ventricle) and then the left atrium contracts (forcing blood into the left ventricle).
Intrinsic regulation is achieved by delaying the contractile signal at the atrioventricular node. This delay also allows the complete contraction of the atria so that the ventricles receive the minimum amount of blood to make their own contractions efficient. A specialized type of neuro-muscular cells, named Purkinje cells, form a system of fibers that covers the heart and which conveys the contractile signal from S-A node (which is also a part of the Purkinje system or subendocardial plexus). Because the Purkinje fibers are slower in passing electrical signals (action potentials) than are neural fibers, the delay allows the atria to finish their contractions prior to ventricular contractions. The signal delay by the AV node lasts about a tenth (0.1) of a second.
The contractile signal then continues to spread across the ventricles via the Purkinje system. The signal travels away from the AV node via the bundle of His before it divides into left and right bundle branches that travel down their respective ventricles.
Extrinsic control of the heart rate and rhythm is achieved via autonomic nervous system (ANS) impulses (regulated by the medulla oblongata) and specific hormones that alter the contractile and or conductive properties of heart muscle. ANS sympathetic stimulation via the cervical sympathetic chain ganglia acts to increase heart rate and increase the force of atrial and ventricular contractions. In contrast, parasympathetic stimulation via the vagal nerve slows the heart rate and decreases the vigor of atrial and ventricular contractions. Sympathetic stimulation also increases the conduction velocity of cardiac muscle fibers. Parasympathetic stimulation decreases conduction velocity.
The regulation in impulse conduction results from the fact that parasympathetic fibers utilize acetylcholine , a neurotransmitter hormone that alters the transmission of an action potential by altering membrane permeability to specific ions (e.g., potassium ions [K+]). In contrast, sympathetic postganglionic neurons secrete the neurotransmitter norepinephrine that alters membrane permeability to sodium (Na+) and calcium ions (Ca2+).
The ion permeability changes result in parasympathetic induced hypopolarization and sympathetic induced hyperpolarization.
Additional hormonal control is achieved principally by the adrenal glands (specifically the adrenal medulla) that release both epinephrine and norepinephrine into the blood when stimulated by the sympathetic nervous system. As part of the fight or flight reflex , these hormones increase heart rate and the volume of blood ejected during the cardiac cycle.
The electrical events associated with the cardiac cycle are measured with an electrocardiogram (EKG). Disruptions in the impulse conduction system of the heart result in arrhythmias.
Variations in the electrical system can lead to serious, even dangerous, consequences. When that occurs an artificial electrical stimulator, called a pacemaker , must be implanted to take over regulation of the heartbeat. The small pacemaker can be implanted under the skin near the shoulder and long wires from it are fed into the heart and implanted in the heart muscle. The pacemaker can be regulated for the number of heartbeats it will stimulate per minute. Newer pacemakers can detect the need for increased heart rate when the individual is under exertion or stress and will respond.
Embryonic development of the human heart
The developing fetal heart accounts for a large percentage of the volume of the early thorax. About 20 days after fertilization , the heart develops from the fusion of paired endothelial tubes into a single tube. Heart growth subsequently involves the growth, expansion, and partitioning of this tube into four chambers separated by thickened septa of cardiac muscle and valves. Atrial development is initially more advanced than ventricular development. The left and right atria develop while the primitive ventricle remains a single chamber. As atrial separation nears completion, the left and right ventricles begin to form, then continue until the heart consists of its fully developed four-chambered structure.
Although the majority of the heart develops from mesoderm (splanchnic mesoderm) near the neural plate and sides of the embryonic disk, there are also contributions from neural crest cells that help form the valves.
Three systems initially return venous blood to the primitive heart. Regardless of the source, this venous blood returns to sinus venosus. Vitelline veins return blood from the yolk sac; umbilical veins return oxygenated blood from the placenta. The left umbilical vein enlarges and passes through the embryonic liver before continuing on to become the inferior vena cava that fuses with a common chambered sinus venosus and the right atrium of the heart. Especially early in development, venous return also comes via the cardinal system. The anterior cardinals drain venous blood from the developing head region. Subcardinal veins return venous blood from the developing renal and urogenital system, while supracardinals drain the developing body wall. The anterior veins empty into the common cardinals that terminate in the sinus venosus.
Movement of blood through the early embryonic vascular system begins as soon as the primitive heart tubes form and fuse. Contractions of the primitive heart begin early in development, as early as the initial fusion of the endothelial channels that fuse to form the heart.
The heart and the atrial tube that form the aorta develop by the compartmentalization of the primitive cardiac tube. Six separate septae are responsible for the portioning of the heart and the development of the walls of the atria and ventricles. A septum primum divides the primitive atria into left and right chambers. The septum secundum (second septum) grows along the same course of the primary septum to add thickness and strength to the partition. There are two holes in these septae through which blood passes, the foramen secundum and the foramen ovale. Specialized endocardinal tissue develops into the atrioventricular septum that separates the atrium and ventricles. The mitral and tricuspid valves also develop from the atrioventricular septum.
As development proceeds, the interventricular septum becomes large and muscular to separate the ventricles and provide strength to these high-pressure contractile chambers. The interventricular septum also has a membranous portion.
Initially, there is only a common truncus arteriosus as a channel for ventricular output. The truncus eventually separates into the pulmonary trunk and the ascending aorta.
Blood oxygenated in the placenta returns to the heart via the inferior vena cava into the right atrium. A valve-like flap in the wall at the juncture of the inferior vena cava and the right atrium directs the majority of the flow of oxygenated blood through the foramen ovale, then allows blood to flow from the right atrium to the left. Although there is some mixing with blood from the superior vena cava, the directed flow of oxygenated blood across the right atrium caused by the valve of the inferior vena cava means that deoxygenated fetal blood returning via the superior vena cava still ends up moving into the right ventricle.
While in the uterus, the lungs are non-functional. Accordingly, another shunt, the ductus arteriosis (also spelled ductus arteriosus) provides a diversionary channel that allows fetal blood to cross between the pulmonary artery and aorta and thus largely bypass the rudimentary pulmonary system.
Because only a small amount of blood returns from the pulmonary circulation, almost all of the blood in the fetal left atrium comes through the foramen ovale. The relatively oxygen-rich blood then passes through the mitral value into the left ventricle. Contractions of the heart, whether in the single primitive ventricle or from the more developed left ventricle, then pump this oxygenated blood into the fetal systemic arterial system.
In response to inflation of the lungs and pressure changes within the pulmonary system, both the foramen ovale and the ductus arteriosis normally close at birth to establish the normal adult circulatory pattern whereby blood flows into the right atrium, though the tricuspid valve into the right ventricle. The right atrium pumps blood into the pulmonary artery and pulmonary circulation for oxygenation in the lungs. Oxygenated blood returns to the left atrium by pulmonary veins. After collecting in the left atrium, blood flows through the mitral value into the left atrium where it is then pumped into the systemic circulation via the ascending aorta.
See also Angiography; Artificial heart and heart valve; Heart diseases; Heart-lung machine; Thoracic surgery; Transplant, surgical.
Resources
books
Gilbert, Scott F. Developmental Biology. 6th ed. Sunderland, Massachusetts: Sinauer Associates, Inc., 2000.
Gray, Henry. Gray's Anatomy. Philadelphia: Lea & Febiger, 1992.
Guyton, Arthur C., and Hall, John E. Textbook of Medical Physiology. 10th ed. Philadelphia: W.B. Saunders Co., 2000.
Kandel, E.R., J.H. Schwartz, and T.M. Jessell. eds. Principles of Neural Science. 4th ed. New York: Elsevier, 2000. Larsen, William J. Human Embryology. 3rd. ed. Philadelphia: Elsevier Science, 2001.
Martini, Frederic H., et al. Fundamentals of Human Anatomy & Physiology. Upper Saddle River, NJ: Prentice Hall, 2001.
Netter, Frank H., and Sharon Colacino. Atlas of the Human Body. Teterboro, NJ: Icon Learning Systems, 2003.
Sadler, T.W., and Jan Langman. Langman's Medical Embryology. 8th ed. New York: Lippincott Williams & Wilkins Publishers, 2000.
Thibodeau, Gary A., and Kevin T Patton . Anatomy & Physiology, 5th ed. St. Louis: Mosby, 2002.
other
Intellimed, Inc. "Human Anatomy Online-Innerbody.com" [cited February, 5, 2003]. <http://www.innerbody.com/htm/body.html> .
Klabunde, R.E. "Cardiac Cycle." Cardiovascular Physiology Concepts. January 17, 2003 [cited January 22, 2003]. <http://www.cvphysiology.com/Heart%20Disease/HD00.htm>.
Murray Jensen College, University Of Minnesota. "Web Anatomy" [cited February 5, 2003]. <http://www.gen.umn.edu/faculty_staff/jensen/1135/webanatomy/>.
Brenda Wilmoth Lerner
K. Lee Lerner
Larry Blaser
Heart
Heart
A heart is a means to circulate blood through the body of an animal. Among the lower species such as insects, arachnids, and others, the heart may simply be an expanded area in a blood vessel and may occur a number of times. The earthworm, for example, has 10 such “hearts.” These areas contract rhythmically to force the blood through the aorta, or blood vessel.
Not until the evolution of the higher vertebrates does the heart achieve its ultimate form, that of a chambered organ with differentiated purposes. Even the lower chordates, such as amphioxus, possess hearts not more advanced than those in the earthworm. It is simply a pulsating blood vessel that moves blood through the body.
Blood
In a complex organism such as a vertebrate, with multiple cell layers and complex organ systems, blood distributes nourishment and oxygen to the cells and removes waste products. Cells within the blood, such as the red blood cells (erythrocytes) and white blood cells (leukocytes) serve specialized functions. The red cells hold and distribute oxygen to release in the cells and return carbon dioxide to the lungs to be eliminated. The white cells carry out immune functions to destroy invading bacteria and other foreign material. Still other components of the blood are involved in forming clots when a blood vessel is opened. The liquid medium, the plasma, carries vitamins and other nutrients throughout the body.
Animals require a means for the blood to obtain oxygen, whether through gills or lungs, and a means to propel the blood through those structures. The heart is central to that purpose.
The multiform heart
The heart is a pulsating organ that pushes a liquid medium throughout the body. It may be as simple as one chamber or as complex as four, as in the higher mammals. In all animals, however, it is an organ that must function day after day without pause to keep the blood moving.
In general, blood from the body or from the oxygen-exchanging structures returns to an atrium, which is simply a holding chamber. The atrium (plural is atria) empties into another chamber called the ventricle, a muscular chamber that contracts rhythmically to propel the blood through the body. Movement of the blood between chambers and in and out of the
heart is controlled by valves that allow movement only in one direction.
Lower vertebrates such as hagfish and other fish have two-chambered hearts. The ventricle pumps blood forward through the gills to obtain oxygen and dispose of carbon dioxide. From there blood enters the dorsal aorta and is carried through the body. The blood returns to the heart by means of the sinus venosus, which empties into the auricle or atrium. From there it is passed into the ventricle and the cycle begins again.
Terrestrial vertebrates such as amphibians have three-chambered hearts and a more complex circulatory system. The third chamber is another auricle or atrium. Unoxygenated blood from the body of the animal returns to the right auricle and the oxygenated blood from the lungs goes into the left auricle. Both contract simultaneously and empty their contents into the single ventricle. The oxygenated and unoxygenated blood does not mix to any degree because of specialized muscle strands in the ventricle. Also, the ventricle contracts immediately after the auricles so the bloods do not have time to mix. When the ventricle contracts, the unoxygenated blood is forced from the heart first and enters the pulmocutaneous vessels leading to the lungs and skin for oxygen exchange. The oxygenated blood enters the truncus arteriosus and flows to the head, arms, body, and hind legs.
Reptiles demonstrate a further step in heart development—a divided ventricle. The wall in the ventricle dividing left from right is incomplete except in crocodiles
and alligators. Blood from the body enters the right auricle from which it passes into the right side of the ventricle and is pumped through the lungs. Oxygenated blood from the lungs enters the left auricle and passes into the left side of the ventricle. From there it moves out through the two aortic arches to the body.
Among the crocodilia, however, a peculiar structure of the aortae allows mixing of arterial and venous blood. The left aortic arch rises from the right side of the heart, as does the pulmonary artery. Thus, unoxy-genated blood pumped from the right ventricle goes to the lungs through the pulmonary artery and also into the aortic arch and out into the body where it will mix with oxygenated blood. The right aortic arch rises from the left ventricle and carries only oxygenated blood.
Birds also possess four-chambered hearts, in this case with complete separation of the two ventricles. They have only one aortic arch, however, and that is the right arch.
Mammals, including humans, also have a four-chambered heart, but the aortic arch curves up and to the left as it leaves the heart. Here, as with birds, there is no mixing of venous and arterial blood (under normal circumstances). Though the heart appears to be a simple organ, it requires a complex series of nerve stimulations, valve openings, and muscle contractions to achieve its purpose.
The human heart
Located in the thoracic cavity, the heart is a four-chambered muscular organ that serves as the primary pump or driving force within the circulatory system. The heart contains a special form of muscle, appropriately named cardiac muscle, that has intrinsic contractility (i.e., is able to beat on its own, without nervous system control).
The Chinese were aware more than 2,000 years ago that the heart is a pump that forces blood through a maze of arteries. The Greeks, however, believed the blood did not circulate at all, and their ideas dominated medical science until the seventeenth century. The Greek physician Galen (c. 130–c. 200) published a great deal on the human body and its functions, much of which was incorrect, but his doctrines held sway for hundreds of years. Not until the 1600s did William Harvey (1578–1657), through human and animal experiments, discover that the heart circulates the blood. He published his findings in 1628, thus bringing Western medical science in line with that of the ancient Chinese.
The human heart on the average weighs about 10.5 oz (300 g). It is a four-chambered, cone-shaped organ about the size of a closed fist that lies in the mid-thorax, under the breastbone (sternum). Nestled between the lungs, the heart is covered by a fibrous sac called the pericardium. This important organ is protected within a bony cage formed by the ribs, sternum, and spine.
In its ceaseless work, the heart contracts some 100,000 times a day to drive blood through about 60,000 mi (96,000 km) of vessels to nourish each of the trillions of cells in the body. Each contraction of the ventricles forces about 2.5 oz (0.075 l) of blood into the circulation, which adds up to about 10 pt (4.7 l) of blood every minute. On average, the heart will pump about 2,500 gal (9,475 l) of blood in a day, and that may go up to as much as 5,000 gal (18,950 l) with exertion. In a lifetime the heart will pump about 100 million gal of blood.
The chambers of the human heart are divided into two upper (superior) atrial chambers and two thicker-walled, heavily muscular inferior ventricular chambers. The right and left sides of the heart are divided by a thick septum. The right side of the heart is on the same side of the heart as is the right arm of the patient. The atrial and ventricular chambers on each side of the septum constitute separate collection and pumping systems for the pulmonary (right side) and systemic circulation (left side). The coronary sulcus or grove separates the atria from the ventricles. The left and right side atrial and ventricular chambers each are separated by a series of one way valves that, when properly functioning, allow blood to move in one direction, but prohibit it from regurgitating (flowing back through the valve).
Deoxygenated blood—returned to the heart from the systemic circulatory venous system—enters the right atrium of the heart through the superior and inferior vena cava. Auricles lie on each atrium and are most visible when the atria are drained and deflated. The auricles (so named because they resembled ear flaps) allow for greater atrial expansion. Pectinate muscles on the auricles assist with atrial contraction. Small contractions within the right atrium, and pressure differences caused by evacuation of blood in the lower (inferior) right ventricle, cause this deoxygenated blood to move through the tricuspid valve during diastole (the portion of the heart’s contractile cycle between contractions, and a period of lower pressure as compared to systole) into the right ventricle. When the heart contracts, a sweeping wave of pressure forces open the pulmonic semilunar valve that allows blood to rush from the right ventricle into the pulmonary artery where it is travels to the lungs for oxygenation and other gaseous exchanges.
Freshly oxygenated blood returns to the heart from the pulmonary circulation through the pulmonary vein the empties into the left atrium. During diastole, the oxygenated blood moves from the left atrium into the left ventricle through the mitral valve. During systolic contraction, the oxygenated blood is pumped under high pressure through the semilunar aortic valve into the aorta and thus, enters the systemic circulatory system.
As the volume and pressure rise during the filling of the right and left ventricles, the increased pressure snaps shut the flaps of the atrioventricular valves (tri-cuspid and mitral valves) anchored by fibrous connection to the left and right ventricles. The pressure in the ventricles seals the valves and as the pressure increases during systole, the valves seal becomes further compressed. A prolapse in one of the valves (a pushing through of one of the cusps) leads to blood flow back through the valve. The cusps are held against prolapse by the chordae tendineae, thin cords that attach the cusps to papillary muscles.
The heart and great vessels attached to it are encased within a multi-layered pericardium. The outer layer is fibrous and covers a double mem-braned inner sac-like structure termed the pericar-dial cavity that is filled with pericardial fluid. The pericardial fluid acts to reduce friction between the heart, the pericardial membranes, and the thoracic wall as the heart contracts and expands during the cardiac cycle.
The heart muscle is composed of three distinct layers. The outermost layer, the outer epicardium, is separated from the inner endocardium by the middle pericardium. The outer epicardium is continuous and in some places the same as the visceral pericardium. Epicardium protects the heart and is invested with capillaries, nerves, and lymph vessels. The middle myocardium is a thick layer of cardiac muscle. The innermost endocardium contains connective tissue and Purkinje fibers. The endocardium is continuous with the lining of the great vessels attached to the heart and it lines all valve and cardiac inner surfaces.
Heart muscle does not directly take up oxygen from the blood it pumps. A specialized set of vessels (e.g., the left and right coronary arteries and their branches) supply oxygenated blood to the heart muscle and constitute the coronary circulation. A heart attack occurs whenever blood flow is occluded (blocked).
The fossa ovalis is a remnant or the embryonic foramen ovale that allows blood to flow between the left and right atria in the developing fetus.
Regulation of the heart
Various intrinsic, neural, and hormonal factors act to influence the rhythm control and impulse conduction within the heart. The rhythmic control of the cardiac cycle and its accompanying heartbeat relies on the regulation of impulses generated and conducted within the heart. Regulation of the cardiac cycle is also achieved via the autonomic nervous system. The sympathetic and parasympathetic divisions of the autonomic system regulate heart rhythm by affecting the same intrinsic impulse conducting mechanisms that lie within the heart in opposing ways.
Cardiac muscle is self-contractile because it is capable of generating a spontaneous electrochemical signal as it contracts. This signal induces surrounding cardiac muscle tissue to contract and a wave-like contraction of the heart can result from the initial contraction of a few localized cardiac cells.
The cardiac cycle describes the normal rhythmic series of cardiac muscular contractions. The cardiac cycle can be subdivided into the systolic and diastolic phases. Systole occurs when the ventricles of the heart contract and diastole occurs between ventricular contractions when the right and left ventricles relax and fill. The sino-atrial node (S-A node) and atrioventricular node (AV node) of the heart act as pacemakers of the cardiac cycle.
The contractile systolic phase begins with a localized contraction of specialized cardiac muscle fibers within the sinoatrial node. The S-A node is composed of nodal tissue that contains a mixture of muscle and neural cell properties. The contraction of these fibers generates an electrical signal that then propagates throughout the surrounding cardiac muscle tissue. In a contractile wave originating at the S-A node, the right atrium muscle contracts (forcing blood into the right ventricle) and then the left atrium contracts (forcing blood into the left ventricle).
Intrinsic regulation is achieved by delaying the contractile signal at the atrioventricular node. This delay also allows the complete contraction of the atria so that the ventricles receive the minimum amount of blood to make their own contractions efficient. A specialized type of neuromuscular cells, named Purkinje cells, form a system of fibers that covers the heart and which conveys the contractile signal from S-A node (which is also a part of the Purkinje system or suben-docardial plexus). Because the Purkinje fibers are slower in passing electrical signals (action potentials) than are neural fibers, the delay allows the atria to finish their contractions prior to ventricular contractions. The signal delay by the AV node lasts about a tenth (0.1) of a second.
The contractile signal then continues to spread across the ventricles via the Purkinje system. The signal travels away from the AV node via the bundle of His before it divides into left and right bundle branches that travel down their respective ventricles.
Extrinsic control of the heart rate and rhythm is achieved via autonomic nervous system (ANS) impulses (regulated by the medulla oblongata) and specific hormones that alter the contractile and or conductive properties of heart muscle. ANS sympathetic stimulation via the cervical sympathetic chain ganglia acts to increase heart rate and increase the force of atrial and ventricular contractions. In contrast, parasympathetic stimulation via the vagal nerve slows the heart rate and decreases the vigor of atrial and ventricular contractions. Sympathetic stimulation also increases the conduction velocity of cardiac muscle fibers. Parasympathetic stimulation decreases conduction velocity.
The regulation in impulse conduction results from the fact that parasympathetic fibers utilize acetylcho-line, a neurotransmitter hormone that alters the transmission of an action potential by altering membrane permeability to specific ions (e.g., potassium ions [K+ ]). In contrast, sympathetic postganglionic neurons secrete the neurotransmitter norepinephrine that alters membrane permeability to sodium (Na+) and calcium ions (Ca2+).
The ion permeability changes result in parasympathetic induced hypopolarization and sympathetic induced hyperpolarization.
Additional hormonal control is achieved principally by the adrenal glands (specifically the adrenal medulla) that release both epinephrine and norepinephrine into the blood when stimulated by the sympathetic nervous system. As part of the fight or flight reflex, these hormones increase heart rate and the volume of blood ejected during the cardiac cycle.
The electrical events associated with the cardiac cycle are measured with an electrocardiogram (EKG). Disruptions in the impulse conduction system of the heart result in arrhythmias.
Variations in the electrical system can lead to serious, even dangerous, consequences. When that occurs an artificial electrical stimulator, called a pacemaker, must be implanted to take over regulation of the heartbeat. The small pacemaker can be implanted under the skin near the shoulder and long wires from it are fed into the heart and implanted in the heart muscle. The pacemaker can be regulated for the number of heartbeats it will stimulate per minute. Newer pacemakers can detect the need for increased heart rate when the individual is under exertion or stress and will respond.
See also Angiography; Artificial heart and heart valve; Heart diseases; Heart-lung machine; Thoracic surgery; Transplant, surgical.
Resources
BOOKS
Gilbert, Scott F. Developmental Biology. 6th ed. Sunderland, Massachusetts: Sinauer Associates, Inc., 2000.
Gray, Henry. Gray’s Anatomy. Philadelphia: Lea & Febiger, 1992.
Guyton, Arthur C., and John E. Hall. Textbook of Medical Physiology. 10th ed. Philadelphia: W.B. Saunders Co., 2000.
Kandel, E.R., J.H. Schwartz, and T.M. Jessell. eds. Principles of Neural Science. 4th ed. New York:Elsevier, 2000.
Larsen, William J. Human Embryology. 3rd. ed. Philadelphia:
Elsevier Science, 2001.
Martini, Frederic H., et al. Fundamentals of Human Anatomy&Physiology. Upper Saddle River, NJ: Prentice Hall, 2001.
Netter, Frank H. and Sharon Colacino. Atlas of the Human Body. Teterboro, NJ: Icon Learning Systems, 2003.
Sadler, T.W., Jan Langman. Langman’s Medical Embryology. 8th ed. New York: Lippincott Williams & Wilkins Publishers, 2000.
Thibodeau, Gary A., and Patton, Kevin T. Anatomy & Physiology. 5th ed. St. Louis: Mosby, 2002.
OTHER
Franklin Institute.“The Heart: An Online Exploration” <http://www.fi.edu/biosci/index.html> (accessed November 27, 2006).
Health Scout Network.“Heart Info.” <http://www.heartinfo.com/> (accessed November 27, 2006).
Intellimed, Inc.“Human Anatomy Online-Innerbody.com” <http://www.innerbody.com/htm/body.html> (February, 5, 2003).
Klabunde, R.E.“Cardiac Cycle.” Cardiovascular Physiology Concepts. January 17, 2003. <http://www.cvphysiology.com/Heart%20Disease/HD002.htm> (accessed March 23, 2007).
Murray Jensen College, University Of Minnesota.“Web Anatomy.” (February 5, 2003) <http://www.gen.umn.edu/faculty_staff/jensen/1135/webanatomy/> (accessed March 23, 2007).
Brenda Wilmoth Lerner
Larry Blaser
heart
The heart is a hollow muscular organ. It acts as the ‘prime mover’ for the circulation of the blood and the maintenance of the blood pressure. A certain volume of blood is delivered with each beat, and a further key aspect is the pressure at which this flow is delivered. Vital functions such as those of lungs and kidneys, or the exchange of components of the blood and tissue fluid at the capillaries, are critically dependent on the pressure achieved within the circulatory system.
Anatomy
The heart comprises a series of blood-filled chambers; the walls are composed virtually entirely of muscle cells of a type unique to the heart (cardiac myocytes). The heart is actually two double pumps acting in series; there are four chambers in all. The right side receives blood returning from the entire body (in the great veins) and pumps it into the pulmonary artery, which supplies only the alveoli (gas exchange sites) in the lungs. The left side receives blood from the lungs and pumps it into the aorta, the largest artery. (The heart is generally illustrated as seen from the front, so ‘left’ and ‘right’ appear mirrored.) The aorta branches to form the arterial tree that supplies blood to the whole body. The heart, appropriately, is itself the first organ supplied with blood from the aorta. The coronary arteries open from the beginning of the aorta and take blood to all parts of the heart tissue. Each side of the heart has an upper chamber, the atrium (plural: ‘atria’), into which the veins drain. They serve as antechambers to the respective ventricles, the thicker-walled chambers that lie below them.Atria and valves
The arrangement of one-way valves and the prevailing pressures mainly determine blood flow from vein–to–atrium–to– ventricle during the cyclic activity of the heart beat, but some pumping of blood by the atria into the ventricles also occurs. The valves preventing back-flow from ventricle to atrium are tough, parachute-like structures partly anchored in the connective tissue plate which forms the physical union of the ventricular and atrial portions of the heart. Their free edges are restrained by several papillary muscles. These are slim extensions from the inner wall of the ventricles, each with a tendinous end fused with the valve; acting like parachute cords, they prevent the valve being pushed through into the atrium as its flaps become filled when the ventricle contracts and puts pressure on its contents. The mitral (or bicuspid) valve on the left side has two flaps, and the tricuspid valve on the right has three. The ‘parachutes’ press together forming a complete closure preventing regress of blood into the respective atrium whence it came. Instead, when the pressure has risen sufficiently, blood is directed into the pulmonary artery and the aorta through one-way valves which separate them from, and prevent back-flow into, their respective ventricles (see Figure).The heart beat
The heart beats between 60 and 220 times per minute in a typical young adult; 40 to 50 million beats per year. The rate alters, often rather obviously, according to one's state of physical and mental activity. This results in pumping over 3 million litres of blood (per year) through the body and an equal volume through the lungs. The pump work done by the heart is equivalent to lifting a 1 kg weight to about twice the height of Mount Everest each day. This level of persistent, rhythmic, and decidedly dynamic activity may provoke a sense of awe, although it is hardly more remarkable than the prosaic activity of every other organ — except in its absolute necessity to keep at it! We will first consider the electrical processes of the heart since, like many muscles, it is triggered into activity (contraction, the heart beat) by an electrical wave. This section is followed by consideration of contraction itself.Electrical aspects
The left and right atria beat virtually simultaneously and then, after a fraction of a second's delay, both ventricles contract. Electrical activity, as in most other muscles, triggers the contraction. This activity arises not from excitatory nerve fibres, but spontaneously within the heart itself from a small clump of pacemaker cells near the point where the vena cava joins the right atrium: the sino-atrial (SA) node. The electrical wave, or action potential, spreads across the heart from cell to cell. This spread is made possible because each heart cell is connected to its immediate neighbours at several contact regions which offer a relatively low resistance to the flow of electrical current. All the muscle cells of the heart are thus electrically linked together. This means that the activity spreads as a wave, its direction determined by the cell-to-cell couplings available. It also means that, as far as we know, every cardiac myocyte is active at some stage during every heart beat. The muscle cells of the atria and ventricles only make electrical contact in one small region, the atrio-ventricular (AV) node at the centre of the heart. Thus, activity follows a predictable, regular path — across the right and left atria, through the AV node, along specialized faster-conducting heart cells (Purkinje fibres) on the internal face of the muscular wall between the two ventricles (interventricular septum), and thence through the substance of both ventricles. Heart cells, like other electrically excitable cells, become inexcitable (refractory) for a brief period after each action potential. Consequently, once the wave has passed right through the ventricles it ceases, since there are no non-refractory cells available to excite. A new wave is spontaneously initiated at the pacemaker region.Contractile (mechanical) aspects
All the heart muscle cells are thus electrically excited and it is this that triggers them to contract. The wave of contraction, therefore, follows the same sequence: atria first, then ventricles. The electrical activity triggers an abrupt rise in the concentration of ‘free’ calcium ions inside the cells — a common feature in signalling contraction in muscle of every type. The calcium ions required are derived in part by influx from the extracellular fluid, in part by release from intracellular stores in the sarcoplasmic reticulum. The influx is through calcium-selective channels in the surface membrane which are opened by the depolarization. The influx itself transiently promotes further influx, and also triggers the release of more calcium from the intracellular store.In each ventricle, as the muscular walls contract (develop tension and shorten) they press upon the blood they enclose. The pressure rises and the AV valve fills out and closes. At this stage of the cycle, the exit valve into the relevant artery (pulmonary artery or aorta) is also closed because the pressure in the arteries is higher than that in the ventricles. Temporarily, each ventricle is thus a closed chamber, it can neither lose nor gain blood, so pressure rises quickly until it exceeds that in the exit artery; the exit valve is then pushed open and blood is ejected, squirted from the ventricles as their muscular walls continue to shorten. The pressure at which the valve opens is much higher on the left side than on the right side, in accordance with the higher blood pressure in the aorta and its branches than in the pulmonary artery and its branches. The resistance offered by the lungs to blood flow is much less than that by the body generally; thus the pressures required of the right ventricle can be lower, yet achieve the same flow rate. Both ventricles eject the same volume of blood (the stroke volume): in the adult heart, about 70 ml (half a teacup) which is half or less of the volume it contained. As action potential finishes, the intracellular calcium concentration has already started to reduce again: some calcium is being ‘pumped’ back into the store, and some is leaving the cell by an ion exchange process. With the raised calcium concentration signal thereby removed, the force of contraction quickly wanes in the muscle, so ventricular pressure falls. The elasticity of the arteries, which were dilated when blood was ejected into them, now ensures that a higher pressure is sustained in them than in the rapidly relaxing ventricles (the ‘garden hose’ effect, familiar to those who have turned off a hose-pipe supply tap only to see water continue squirting as the elastic pipe collapses). The respective exit valves are thus pushed closed again, preventing reflux into the ventricles. Blood pressure, therefore, falls more slowly in the arteries than in the ventricles. At this stage about 90 ml of blood remains in each ventricle. Pressure continues to fall quickly until it is below that in the atria. Thus, the AV valves are pushed open, allowing blood to flow from the atria into the ventricles ‘topping them up’ with more blood. (Despite the appearance in some published schematic diagrams and ‘cartoon’ sequences, at all stages of the heart beat the chambers are ‘full’ of blood. It is the enclosed volume which changes, depending on the tension and elasticity of the muscular walls and the status of the inlet and outlet valves.)
The return of the ventricle to its ‘resting’ shape between beats is due to its own elasticity. Like a squeezed sponge or hollow rubber ball, this significantly ‘sucks’ blood from the atria, thereby contributing to its own filling. The reduction of this factor in old age or its enhancement by athletic training have a major effect on overall cardiac function. These effects are analogous to problems associated with ‘stiff’ inelastic valves which perhaps more obviously compromise effective flow in and out of the chambers of the heart.
The state when the heart is contracting is termed systole (sis'-toe-lee); the relaxed state is termed diastole (di-a'-stoe-lee).
Control of pump function
The cardiac output is the volume of blood pumped per minute by each ventricle — some 5 litres/minute at ‘rest’ — and is simply the product of heart rate and stroke volume. Cardiac output will thus alter if either varies. The stroke volume is in turn influenced by cardiac filling and by the contractility of the cardiac muscle itself — its intrinsic ability to contract (shorten and/or produce tension).Heart rate
The earliest human hunters will have noticed, like later horror film makers, that even when removed from the body, the heart continues to beat for a time. Other organs also continue to live, but their activity is hardly as impressive as that of the heart.Because all the cells of the heart are electrically connected to their neighbours, the whole behaves as a unit. Most regions are inactive, unless artificially stimulated. The activity of the regions with the property of ‘firing’ spontaneously is conducted to all their inactive neighbours, so they act as pacemakers. The inherent pacemaker firing rate, typically about 100 per minute, is influenced by nerve actions of the autonomic nervous system: sympathetic nerves release noradrenaline which increases rate, and parasympathetic (vagus) nerve fibres release acetylcholine which slows the rate. Heart rate typically varies between 60 per minute (in deep sleep) to approaching 200 per minute (during brief bursts of maximal exercise). The normal ‘resting’ rate while sitting, relaxed, is about 70 per minute, but shows wide variation amongst entirely healthy individuals. (In one university class of 350 twenty-year-old students, the range was 48 to 90 per minute.) One common feature is a marked variation within the breathing cycle: breathing in usually increases the rate. Physical fitness, particularly that associated with endurance rather than muscle strength, is often associated with a low resting rate. Extremes such as the tennis player Bjorn Borg, or the professional cyclist Miguel Indurain, with resting values in the low 30s per minute, are well known. Young children have higher resting rates; whilst still in the womb, a baby will have a rate of 120 to 160 beats per minute; it is often reported that rates above 140 indicates a female baby, but there are more reliable tests!
Cardiac filling
‘Filling’ reflects the flow of blood back into the heart (venous return from the lungs and the body). William Harvey observed that the presence of valves requires that blood in the larger veins can only flow towards the heart, the key to recognizing that blood circulates. Amongst other factors, the extent of muscular activity, breathing movements, and body positions (standing, lying, arms or legs raised) all affect the rate of return of blood to the heart. Cardiac muscle shows the unusual property that, within limits, it contracts more powerfully when starting from stretched lengths, so that the ventricle ‘empties’ more forcibly when it is ‘filled’ more than usual. This is achieved at trivial extra metabolic cost; the efficiency of pumping thus increases as output increases; surely a paradigm for ‘productivity gains’. This property allows the heart to compensate automatically when the volume of blood within it at the start of the beat (the end diastolic volume) is greater than previously, by pumping more forcefully, thus ejecting a larger volume. This feature is termed Starling's ‘Law of the Heart’, after one of its discoverers.Contractility
It is obvious that an intrinsically stronger heart will be able to eject blood more forcefully and more completely. Unlike our voluntary (skeletal) muscles, the ‘strength’ of heart muscle can vary quickly, even from one beat to the next. This is because it is sensitive to chemical influences (especially of adrenaline/noradrenaline) and electrical influences that can rapidly modify the intracellular processes that underlie contraction. Additionally, as with voluntary muscle, the extent of growth and development of the heart muscle will affect the overall strength of the organ; athletes generally have thicker heart walls which match the larger muscles in their thicker limbs. A normal, sudden increase in contractility is associated with the onset of physical activity or even with its anticipation; this is signalled to the heart, along with the increase in heart rate, by activity in the sympathetic nerve fibres which release noradrenaline. The combination of higher rate and stronger, more rapid contraction tends to match cardiac output to the increased ‘demands’ for blood flow to the exercising muscles.The heart of the matter and the matter of the heart
The control systems which influence the heart rate and strength of beating are the same as those implicated in such apparently diverse processes as blushing, breathing rate, sexual arousal, mental stress, or alertness. These links seem to have been recognized by our forebears in advance of the definitive precision of the discoveries of cardiovascular physiology. Poets report that hearts leap, hearts are strong, hearts are united, hearts are hot, heart strings are plucked, hearts are ‘in the mouth’, hearts become feeble, hearts are chilled, hearts tremble, and hearts are broken. In human history, the nature of the circulation of the blood and the (quite literally) central role of the heart in this system are still recent discoveries, even though they rank with the very earliest of the truly ‘modern’ scientific method. Nevertheless, the heart (with perhaps the eye) is the organ most quoted in literature and song to define the essential qualities of life and even its very presence. The ready perception of the action of the heart, its racing rate when we are excited or surprised, aroused or shocked, the shallow, rapid beat encountered in feverish poor health, the occasional irregularity of beat that can concern us all (often, thankfully, quite unnecessarily), together form the shared ‘heart’ experiences of mankind that writers and poets have ever drawn upon. We are generally blissfully unaware of the other hives of metabolic industry that contribute to our physiology. The liver, the thyroid, the hypothalamus, the pituitary, the spleen, the pancreas, not one of these is dignified with a property recognizable to their owners. It is surely the literal vitality of the heart's rhythmic beating, the recognition of its link to the movements of blood, the necessary identity between this continual activity and life itself (outside an operating theatre) that validates the continuing truth of poetic notions of ‘heart’David J. Miller
See cardiovascular system.See also autonomic nervous system; blood pressure; blood circulation; blood vessels; cardiac muscle; heart attack; heart block; heart failure; heart sound.
Heart
Heart
Definition
The heart is a muscular organ of the cardiovascular system that contracts to cause movement of the blood throughout the body.
Description
The heart is approximately fist-sized and located in the chest between the two lungs and behind the ribs and breastbone (sternum). It rests at a slight tilt from vertical, which makes it appear to be on the left side of the body. The walls of the heart are made up of three layers of tissue: epicardium, myocardium, and endocardium. The epicardium is a thin layer on the outer surface of the heart. The myocardium is the muscular layer, made up of cardiac muscle that contracts to do the work of the heart moving the blood. The endocardium is the smooth inner lining of the heart.
The entire structure of the heart is enclosed in a fibrous sac called the pericardium. A small amount of liquid is normally found in the space between the heart and the pericardium, which helps reduce the friction between the epicardial and pericardial membranes.
The heart is divided by a central wall (or septum) into its right and left sides. Each of these sides contains a smaller, upper chamber known as an atrium, and a lower, larger chamber known as a ventricle. The atria and ventricles are separated by a valve made of flaps of tissue that prevent blood flow in the wrong direction. The valve on the left side of the heart is the mitral (or bicupsid) valve, which has two flaps. The right atria and ventricle are separated by the tricupsid valve, which has three flaps.
There are five great vessels branching off from the heart that are responsible for carrying blood into or out of the organ. These five vessels are the aorta, the pulmonary artery and vein, and the superior and inferior venae cavae. The aorta is the main artery, carrying oxygenated blood from the heart out into the body. The pulmonary artery carries blood away from the heart to the lungs, and the pulmonary vein carries blood from the lungs to the heart. The superior and inferior venae cavae carry deoxygenated blood from the upper and lower parts of the body back to the heart.
Unidirectional valves separate two of the great vessels from the chambers of the heart. The pulmonic (or pulmonary valve) separates the right ventricle and the pulmonary artery. The aorta and left ventricle are separated by the aortic valve.
The coronary arteries are two vessels that divide off the aorta and branch out over the entire surface of the heart. These vessels bring oxygenated blood to the heart tissue itself.
Function
The heart functions as a strong, four-chambered muscular pump. It can move more than five quarts of blood through the body each minute, the equivalent of about 2,000 gallons per day. At a typical heart rate of 72 beats per minute, the heart contracts on average 100,000 times per day. This adds up to more than 2.5 billion beats in a 70-year lifetime.
One key to the functioning of the heart is the unique characteristics of its muscular tissue. Cardiac muscle differs from other muscles of the body in that its normal function is a rhythmic contraction, which is the basis for the tissue's ability to respond to the electrical impulses that govern the beating of the heart. The natural pacemaker of the heart, the sinoatrial (SA) node, is located in the right atrium. Cardiac muscle cells that naturally contract at the fastest rate when compared to the other cells of the heart surround this cluster of nerve cells. This area of the heart therefore has the ability to initiate the contraction by sending wavelike electrical signals throughout the organ.
First, the electrical signal causes the two atria to contract, when sends the blood from those chambers into the two ventricles. Then the signal passes down through a group of nerve cells known as the atrioventricular (AV) node. This nerve cluster is located near the center of the heart. The travel through this area slows down the signal so that it reaches the ventricles after the atria have finished their contraction. Then the ventricles contract, moving the blood out of the heart, and the cycle starts again. The heart's electrical activity can be measured using electrocardiography .
The physical functions of the full heartbeat is known as the cardiac cycle . The cycle can be divided into two phases: diastole and systole. Diastole occurs when the heart relaxes and the myocardial fibers lengthen. As the heart dilates, the cavities fill with blood. Diastole of the atria occurs slightly before the diastole of the ventricles.
Systole happens when the part of the heart is in contraction and the myocardial fibers shorten. Again, systole of the atria precedes systolic phase of the ventricles. Systole of the ventricles cause blood to surge out of the heart and into the aorta and pulmonary artery.
Over time, the cardiac cycle occurs as follows. It begins with the diastole of the atrium, where both the left and right atria relax and fill with blood. The right atria fills with deoxygenated blood from the superior and inferior venae cavae. The pulmonary artery fills the left atria with newly oxygenated blood from the lungs. The SA node signals the beginning of systole and the atrium contract, sending blood through the tricuspid and mitral valves into the right and left ventricles, respectively. During ventricle filling, the valves of the great vessels are closed so blood already pumped out of the heart does not leak back.
The electrical signal has now reached the ventricles and they contract, sending the deoxygenated blood of the right ventricle into the pulmonary artery to the lungs and the oxygenated blood of left ventricle into the aorta to the body. During contraction, the tricupsid and mitral valves close to prevent flow back into the atrium. This cycle is repeated continuously.
Role in human health
The heart is the centerpiece of the elaborate and extensive human cardiovascular system. Responsible for moving the blood throughout the body, this system transports the necessities for life—oxygen, nutrients, hormones, immune functions—to the cells. The system also transports wastes such as carbon dioxide away from the cells to the organs responsible for their elimination from the body. The heart is the driving force behind this essential
KEY TERMS
Diastole —Phase of the heartbeat where the ventricles relax and fill with blood.
Endocardium —The thin, innermost layer of the heart.
Epicardium —The outermost layer of the heart.
Myocardium —The middle, working layer of the heart containing the heart muscle cells.
Regurgitation —A defect of the heart valves that interferes with its ability to close completely, allowing blood to leak in the direction opposite of circulation.
Septum —A physical divider between chambers, found between the atria and the ventricles.
Stenosis —A stiffening of the heart valves, which narrows its opening and can interfere with function.
Systole —Phase of the heartbeat where the ventricles contract and force blood from the heart.
transport. Therefore it is not surprising that a healthy heart is necessary for a healthy body.
There are several risk factors for heart problems that can be controlled through preventative measures. These include lowering blood cholesterol levels with diet, exercise , or in extreme cases, medications. Lower cholesterol levels lower the probability of coronary artery disease (clogging of the arteries that bring oxygenated blood to the heart), a major cause of heart failure . Keeping blood pressure , blood sugar levels, and body weight within normal levels also greatly decreases the chance for heart problems. Other controllable risk factors include a sedentary lifestyle, stress and anger, and smoking.
Common diseases and disorders
According to 1999 estimates, approximately 58.8 million Americans have one or more types of heart disease, as it is most broadly defined. Although the cause and effect of various heart diseases can be examined in a particular patient, it is difficult to make generalizations about different diseases and disorders. Often one disease of the cardiovascular system will contribute or even cause another. In any case, the various symptoms of an unhealthy heart, whatever the cause, are quite common.
Several diseases of the heart are related to athero-sclerosis, the accumulation of cholesterol in the arteries. When this problem occurs in the coronary arteries, it is known as coronary artery disease. Three conditions which can follow from the loss of blood flow to the heart due to the clogged arteries are angina pectoris, a severe chest pain , myocardial infarction (commonly called a heart attack), or congestive heart failure, where the heart is unable to efficiently pump the blood throughout the body.
Angina pectoris is the result of temporary deprivation of oxygen and often occurs after stress or exertion. Heart attacks occur because a portion of the heart is permanently deprived of blood and the cells become damaged. Congestive heart failure involves a cascade reaction of the body to inefficient heart action that results in accumulation of fluids in the outer reaches of the body. In each of these cases, the trigger cause of the condition was the blockage of the arteries that supply the heart.
A second set of heart diseases involves an abnormality in the electrical system of the heart. Called arrhythmias, these diseases occur when the heart no longer beats in the standard pattern. Altered beat function can greatly reduce the efficiency of the heart and can result in fainting (due to lack of blood to the brain ), palpitations (an unpleasant awareness of the beating of the heart), shortness of breath, and chest pain. Some common types of arrhythmia include brachycardia (slow heart beat), atrial fibrillation, and ventricular fibrillation.
Brachycardia is commonly treated using pacemakers , an inplanted device that keeps the heart's rhythm steady. Fibrillations are very fast, inefficient beats of the atrium or ventricles. Fibrillation can be treated with medication or an implanted cardiac defibrillator (ICD) that delivers a shock to the heart to restart normal beating. Arrhythmias can be caused by coronary heart disease, high blood pressure, or a previous heart attack, emphasizing the interrelation of the various heart diseases.
A third kind of heart disease involves damage to one of the four valves of the heart. The frequency of damage to these structures is related to the work that they do—with the structures undergoing the greatest amount of pressure having the highest frequency of disease. Thus, valve problems occurs most frequently with the mitral valve, then the aortic, tricupsid, and pulmonic. Mitral valve prolapse is the most common condition, where excess valve tissue prevents it from closing properly. Surgery may not be necessary, however, until leaking of the valve, known as valve regurgitation, accompanies the prolapse. Regurgitation is a symptom of stenosis, a condition where the valve has become too stiff to function properly.
Untreated rheumatic fever , a bacterial infection , is the most prevalent cause of valve problems. The use ofantibiotics to treat strep throat has greatly reduced the incidence of this disease in the United States. Congential defects are the second most common cause of heart valve conditions.
Congenital heart defects, in the valves and other structures, occur when the heart or its vessels do not develop normally before birth. The most common congenital heart defect is a combination of four problems called the teralogy of Fallot. With this problem the ventricular septum is incomplete, there is an obstruction to blood flow beneath the pulmonary artery, the aorta is shifted rightward, and the right ventricular wall is thickened.
A final kind of heart disease is cardiomyopathy. This disorder occurs when the muscle of the heart degenerates. There are multiple causes of cardiomyopathy and it is the number one reason people undergo heart transplants. Categorized by the type of muscle damage, there are three general types of cardiomyopathy: dilated, hypertrophic, and restrictive. Dilated cardiomyopathy refers to the enlargement of the heart that is a response to the overall myocardial weakness. Many problems can cause dilated cardiomyopathy including viral infections, excessive alcohol intake, and myocarditis (inflammation of the heart).
Hypertrophic cardiomyopathy is an abnormal over-growth of the heart muscle. An inherited disease, the overgrown muscle blocks the movement of blood both into and out of the heart. Restrictive cardiomyopathy is due to a stiffening of the heart muscle that prevents it from fully relaxing during diastole. This problem is a symptom of other diseases such as hemochromatosis (a defect in iron use by the body) or amyloidosis (overproduction of antibodies by the bone marrow that cannot be broken down).
Resources
BOOKS
Baum, Seth J. The Total Guide to a Healthy Heart. New York: Kensington Books, 1999.
Topol, Eric J., ed. Cleveland Clinic Heart Book. New York: Hyperion, 2000.
PERIODICALS
Crumlish, Christine, et al. "When Time is Muscle." American Journal of Nursing 100 (January 2000): 26.
Thomas, Donna Jean G., and Barbara F. Harrah, "A New Look at Heart Failure." Home Healthcare Nurse 18 (March 2000).
ORGANIZATIONS
American Heart Association. 7272 Greenville Avenue, Dallas, Texas 75231. (800) AHA-USA1. <http://www.americanheart.org>.
OTHER
Heart Information Network. June 29, 2001. <http://www.heartinfo.org> (July 2, 2001).
Michelle L. Johnson, M.S., J.D.
Heart
Heart
Definition
The heart is a muscular organ of the cardiovascular system that contracts to cause movement of the blood throughout the body.
Description
The heart is approximately fist-sized and located in the chest between the two lungs and behind the ribs and breastbone (sternum). It rests at a slight tilt from vertical, which makes it appear to be on the left side of the body. The walls of the heart are made up of three layers of tissue: epicardium, myocardium, and endocardium. The epicardium is a thin layer on the outer surface of the heart. The myocardium is the muscular layer, made up of cardiac muscle that contracts to do the work of the heart moving the blood. The endocardium is the smooth inner lining of the heart.
The entire structure of the heart is enclosed in a fibrous sac called the pericardium. A small amount of liquid is normally found in the space between the heart and the pericardium, which helps reduce the friction between the epicardial and pericardial membranes.
The heart is divided by a central wall (or septum) into its right and left sides. Each of these sides contains a smaller, upper chamber known as an atrium, and a lower, larger chamber known as a ventricle. The atria and ventricles are separated by a valve made of flaps of tissue that prevent blood flow in the wrong direction. The valve on the left side of the heart is the mitral (or bicuspid) valve, which has two flaps. The right atria and ventricle are separated by the tricuspid valve, which has three flaps.
There are five great vessels branching off from the heart that are responsible for carrying blood into or out of the organ. These five vessels are the aorta, the pulmonary artery and vein, and the superior and inferior venae cavae. The aorta is the main artery, carrying oxygenated blood from the heart out into the body. The pulmonary artery carries blood away from the heart to the lungs, and the pulmonary vein carries blood from the lungs to the heart. The superior and inferior venae cavae carry deoxygenated blood from the upper and lower parts of the body back to the heart.
Unidirectional valves separate two of the great vessels from the chambers of the heart. The pulmonic (or pulmonary valve) separates the right ventricle and the pulmonary artery. The aorta and left ventricle are separated by the aortic valve.
The coronary arteries are two vessels that divide off the aorta and branch out over the entire surface of the heart. These vessels bring oxygenated blood to the heart tissue itself.
Function
The heart functions as a strong, four-chambered muscular pump. It can move more than five quarts of blood through the body each minute, the equivalent of about 2,000 gallons (7,570 L) per day. At a typical heart rate of 72 beats per minute, the heart contracts on average 100,000 times per day. This adds up to more than 2.5 billion beats in a 70-year lifetime.
One key to the functioning of the heart is the unique characteristics of its muscular tissue. Cardiac muscle differs from other muscles of the body in that its normal function is a rhythmic contraction, which is the basis for the tissue's ability to respond to the electrical impulses that govern the beating of the heart. The natural pacemaker of the heart, the sinoatrial (SA) node, is located in the right atrium. Cardiac muscle cells that naturally contract at the fastest rate when compared to the other cells of the heart surround this cluster of nerve cells. This area of the heart therefore has the ability to initiate the contraction by sending wavelike electrical signals throughout the organ.
First, the electrical signal causes the two atria to contract, when sends the blood from those chambers into the two ventricles. Then the signal passes down through a group of nerve cells known as the atrioventricular (AV) node. This nerve cluster is located near the center of the heart. The travel through this area slows down the signal so that it reaches the ventricles after the atria have finished their contraction. Then the ventricles contract, moving the blood out of the heart, and the cycle starts again. The heart's electrical activity can be measured using electrocardiography.
The physical functions of the full heartbeat is known as the cardiac cycle. The cycle can be divided into two phases: diastole and systole. Diastole occurs when the heart relaxes and the myocardial fibers lengthen. As the heart dilates, the cavities fill with blood. Diastole of the atria occurs slightly before the diastole of the ventricles. Systole happens when the part of the heart is in contraction and the myocardial fibers shorten. Again, systole of the atria precedes systolic phase of the ventricles. Systole of the ventricles cause blood to surge out of the heart and into the aorta and pulmonary artery.
Over time, the cardiac cycle occurs as follows. It begins with the diastole of the atrium, where both the left and right atria relax and fill with blood. The right atria fills with deoxygenated blood from the superior and inferior venae cavae. The pulmonary artery fills the left atria with newly oxygenated blood from the lungs. The SA node signals the beginning of systole and the atrium contract, sending blood through the tricuspid and mitral valves into the right and left ventricles, respectively. During ventricle filling, the valves of the great vessels are closed so blood already pumped out of the heart does not leak back.
The electrical signal has now reached the ventricles and they contract, sending the deoxygenated blood of the right ventricle into the pulmonary artery to the lungs and the oxygenated blood of left ventricle into the aorta to the body. During contraction, the tricuspid and mitral valves close to prevent flow back into the atrium. This cycle is repeated continuously.
Role in human health
The heart is the centerpiece of the elaborate and extensive human cardiovascular system. Responsible for moving the blood throughout the body, this system transports the necessities for life—oxygen, nutrients, hormones, immune functions—to the cells. The system also transports wastes such as carbon dioxide away from the cells to the organs responsible for their elimination from the body. The heart is the driving force behind this essential transport. Therefore it is not surprising that a healthy heart is necessary for a healthy body.
There are several risk factors for heart problems that can be controlled through preventative measures. These include lowering blood cholesterol levels with diet, exercise, or in extreme cases, medications. Lower cholesterol levels lower the probability of coronary artery disease (clogging of the arteries that bring oxygenated blood to the heart), a major cause of heart failure. Keeping blood pressure, blood sugar levels, and body weight within normal levels also greatly decreases the chance for heart problems. Other controllable risk factors include a sedentary lifestyle, stress and anger, and smoking.
Common diseases and disorders
According to 1999 estimates, approximately 58.8 million Americans have one or more types of heart disease, as it is most broadly defined. Although the cause and effect of various heart diseases can be examined in a particular patient, it is difficult to make generalizations about different diseases and disorders. Often one disease of the cardiovascular system will contribute or even cause another. In any case, the various symptoms of an unhealthy heart, whatever the cause, are quite common.
Several diseases of the heart are related to atherosclerosis, the accumulation of cholesterol in the arteries. When this problem occurs in the coronary arteries, it is known as coronary artery disease. Three conditions which can follow from the loss of blood flow to the heart due to the clogged arteries are angina pectoris, a severe chest pain; myocardial infarction, commonly called a heart attack; or congestive heart failure, in which the heart is unable to efficiently pump the blood throughout the body.
Angina pectoris is the result of temporary deprivation of oxygen and often occurs after stress or exertion. Heart attacks occur because a portion of the heart is permanently deprived of blood and the cells become damaged. Congestive heart failure involves a cascade reaction of the body to inefficient heart action that results in accumulation of fluids in the outer reaches of the body. In each of these cases, the trigger cause of the condition was the blockage of the arteries that supply the heart.
A second set of heart diseases involves an abnormality in the electrical system of the heart. Called arrhythmias, these diseases occur when the heart no longer beats in the standard pattern. Altered beat function can greatly reduce the efficiency of the heart and can result in fainting (due to lack of blood to the brain ), palpitations (an unpleasant awareness of the beating of the heart), shortness of breath, and chest pain. Some common types of arrhythmia include brachycardia (slow heart beat), atrial fibrillation, and ventricular fibrillation.
Brachycardia is commonly treated using pacemakers, implanted devices that keep the heart's rhythm steady. Fibrillations are very fast, inefficient beats of the atrium or ventricles. Fibrillation can be treated with medication or an implanted cardiac defibrillator (ICD) that delivers a shock to the heart to restart normal beating. Arrhythmias can be caused by coronary heart disease, high blood pressure, or a previous heart attack, emphasizing the interrelation of the various heart diseases.
A third kind of heart disease involves damage to one of the four valves of the heart. The frequency of damage to these structures is related to the work that they do—with the structures undergoing the greatest amount of pressure having the highest frequency of disease. Thus, valve problems occurs most frequently with the mitral valve, then the aortic, tricuspid, and pulmonic. Mitral valve prolapse is the most common condition, where excess valve tissue prevents it from closing properly. Surgery may not be necessary, however, until leaking of the valve, known as valve regurgitation, accompanies the prolapse. Regurgitation is a symptom of stenosis, a condition where the valve has become too stiff to function properly.
Untreated rheumatic fever, a bacterial infection, is the most prevalent cause of valve problems. The use of antibiotics to treat strep throat has greatly reduced the incidence of this disease in the United States. Congential defects are the second most common cause of heart valve conditions.
KEY TERMS
Diastole— Phase of the heartbeat where the ventricles relax and fill with blood.
Endocardium— The thin, innermost layer of the heart.
Epicardium— The outermost layer of the heart.
Myocardium— The middle, working layer of the heart containing the heart muscle cells.
Regurgitation— A defect of the heart valves that interferes with its ability to close completely, allowing blood to leak in the direction opposite of circulation.
Septum— A physical divider between chambers, found between the atria and the ventricles.
Stenosis— A stiffening of the heart valves, which narrows its opening and can interfere with function.
Systole— Phase of the heartbeat where the ventricles contract and force blood from the heart.
Congenital heart defects, in the valves and other structures, occur when the heart or its vessels do not develop normally before birth. The most common congenital heart defect is a combination of four problems called the teralogy of Fallot. With this problem the ventricular septum is incomplete, there is an obstruction to blood flow beneath the pulmonary artery, the aorta is shifted rightward, and the right ventricular wall is thickened.
A final kind of heart disease is cardiomyopathy. This disorder occurs when the muscle of the heart degenerates. There are multiple causes of cardiomyopathy and it is the number one reason people undergo heart transplants. Categorized by the type of muscle damage, there are three general types of cardiomyopathy: dilated, hypertrophic, and restrictive. Dilated cardiomyopathy refers to the enlargement of the heart that is a response to the overall myocardial weakness. Many problems can cause dilated cardiomyopathy including viral infections, excessive alcohol intake, and myocarditis (inflammation of the heart).
Hypertrophic cardiomyopathy is an abnormal overgrowth of the heart muscle. An inherited disease, the overgrown muscle blocks the movement of blood both into and out of the heart. Restrictive cardiomyopathy is due to a stiffening of the heart muscle that prevents it from fully relaxing during diastole. This problem is a symptom of other diseases such as hemochromatosis (a defect in iron use by the body) or amyloidosis (overproduction of antibodies by the bone marrow that cannot be broken down).
Resources
BOOKS
Baum, Seth J. The Total Guide to a Healthy Heart. New York: Kensington Books, 1999.
Topol, Eric J., ed. Cleveland Clinic Heart Book. New York: Hyperion, 2000.
PERIODICALS
Crumlish, Christine, et al. "When Time is Muscle." American Journal of Nursing 100 (January 2000): 26.
Thomas, Donna Jean G., and Barbara F. Harrah, "A New Look at Heart Failure." Home Healthcare Nurse 18 (March 2000).
ORGANIZATIONS
American Heart Association. 7272 Greenville Avenue, Dallas, Texas 75231. (800) AHA-USA1. 〈http://www.americanheart.org〉.
OTHER
Heart Information Network. June 29, 2001. 〈http://www.heartinfo.org〉 (July 2, 2001).
Heart
Heart
In humans, the heart is a pulsating organ that pumps blood throughout the body. On average, the heart weighs about 10.5 ounces (300 grams). It is a four-chambered, cone-shaped organ about the size of a closed fist. It lies under the sternum (breastbone), nestled between the lungs. The heart is covered by a triple-layered, fibrous sac called the pericardium. This important organ is protected within a bony cage formed by the ribs, sternum, and spine.
Words to Know
Angina pectoris: Chest pain that occurs when blood flow to the heart is reduced, resulting in a shortage of oxygen.
Aorta: Largest blood vessel in the body.
Atherosclerosis: Condition in which fatty material such as cholesterol accumulates on an artery wall forming plaque that obstructs blood flow.
Atrioventricular node: Area of specialized tissue that lies near the bottom of the right atrium that fires an electrical impulse across the ventricles, causing them to contract.
Atria: Upper heart chambers that receive blood.
Diastole: Period of relaxation and expansion of the heart when its chambers fill with blood.
Mitral valve: Valve with two cusps that separates the left atrium from the left ventricle.
Pericardium: Fibrous sac that encloses the heart.
Sinoatrial node: Area of specialized tissue in the upper area of the right atrium that fires an electrical impulse across the atria, causing them to contract.
Systole: Rhythmic contraction of the heat.
Tricuspid valve: Fibrous, three-leaflet valve that separates the right atrium from the right ventricle.
Ventricles: Lower heart chambers that pump blood.
In its ceaseless work, the heart contracts more than 100,000 times a day to drive blood through about 60,000 miles (96,000 kilometers) of vessels to nourish each of the trillions of cells in the body. Each contraction of the heart forces about 2.5 ounces (74 milliliters) of blood into the bloodstream. This adds up to about 10 pints (4.7 liters) of blood every minute. An average heart will pump about 1,800 gallons (6,800 liters) of blood each day. With exercise, that amount may increase as much as six times. In an average lifetime, the heart will pump about 100 million gallons (380 million liters) of blood.
The heart is divided into four chambers. The upper chambers are the atria (singular atrium). The lower chambers are the ventricles. The wall that divides the right and left sides of the heart is the septum. The atria are thin-walled holding chambers for blood that returns to the heart from the body. The ventricles are muscular chambers that contract rhythmically to propel blood through the body.
Movement of blood between chambers and in and out of the heart is controlled by valves that allow movement in only one direction. Between the atria and ventricles are atrioventricular (AV) valves. Between the ventricles and the major arteries into which they pump blood are semilunar (SL) valves. The "lub-dup" sounds that a physician hears through a stethoscope occur when the heart valves close. The AV valves produce the "lub" sound upon closing, while the SL valves cause the "dup" sound.
Movement of blood through the heart
Blood carrying no oxygen (oxygen-depleted) returns to the right atrium of the heart through the vena cava, a major vein. It then passes through the tricuspid or right AV valve into the right ventricle. The tricuspid valve is so named because it has three cusps or flaps that open and close to control the flow of blood. When the right ventricle contracts, blood is forced from the heart into the pulmonary artery through the pulmonary SL valve.
The pulmonary artery is the only artery in the body that carries oxygen-depleted blood. It carries this blood into the lungs, where the blood releases carbon dioxide and other impurities and picks up oxygen. The freshly oxygenated blood then returns to the left atrium through the four pulmonary veins. The blood then passes through the mitral or left AV valve into the left ventricle.
The left ventricle has the hardest task of any chamber in the heart. It must force blood from the heart into the body and head. For that purpose it has a much thicker wall, approximately three times thicker than the wall of the right ventricle. When the left ventricle contracts, blood passes through the aortic SL valve into the largest artery in the body—the aorta—to be carried and distributed to every area of the body.
The heart muscle or myocardium is unique in that it is not under voluntary control (a person cannot cause it to start and stop at will) and it must work without ceasing for a lifetime. The myocardium requires a great deal of nourishment, and the arteries that feed it are the first to branch off from the aorta. These coronary arteries pass down and over the heart, providing it with an abundant and uninterrupted blood supply.
The heart cycle and nerve impulses
Each heartbeat or heart cycle (also known as the cardiac cycle) is divided into two phases. The two atria contract while the two ventricles relax. Then, the two ventricles contract while the two atria relax. The contraction phase is known as systole, while the relaxation phase is known as diastole. The heart cycle consists of a systole and diastole of both the atria and ventricles. At the end of a heartbeat all four chambers rest.
The pattern of heart chambers filling and emptying in sequence is controlled by a system of nerve fibers. They provide the electrical stimulus to trigger contraction of the heart muscle. The initial stimulant is provided by a small strip of specialized tissue in the upper area of the right atrium. This is called the sinoatrial or SA node. The SA node fires an electrical impulse that spreads across the atria, causing them to contract. The impulse also reaches another node, the atrioventricular or AV node. (The AV node lies near the bottom of the right atrium just above the ventricle.) After receiving the SA impulse, the AV node sends out its own electrical impulse. The AV impulse travels down a specialized train of fibers into the ventricular muscle, causing the ventricles to contract. In this way, the contraction of the atria occur slightly before the contraction of the ventricles.
The electrical activity of the heart can be measured by a device called the electrocardiograph (EKG). Variations in the heart's electrical system can lead to serious, even dangerous, consequences. When that occurs, an electrical stimulator called an artificial pacemaker must be implanted to take over the regulation of the heartbeat. The small pacemaker can be implanted under the skin near the shoulder. Long wires from the pacemaker are fed into the heart and implanted in the heart muscle. The pacemaker can be regulated for the number of heartbeats it will stimulate per minute. Newer pacemakers can detect the need for increased heart rate when the individual is exercising or under stress.
Heart diseases
Heart disease is the number-one cause of death among people living in the industrial world. Preventive measures, such as an improved diet and regular exercise, are the best methods to overcome heart disease.
Congenital heart disease is any defect in the heart present at birth. About 1 out of every 100 infants are born with some sort of heart abnormality. Many of these congenital defects do not need to be treated. The most common type of congenital heart disease is the atrial septal defect. In this condition, an opening in the septum between the right and left atria allows blood from the two chambers to mix. If the hole is small, it does not cause a problem. But a larger opening that allows too much blood to mix can cause the right ventricle to be overwhelmed with blood,
a condition that eventually leads to heart failure. The defect can be corrected through a surgical procedure in which a patch is placed over the opening to seal it.
Coronary heart disease (also known as coronary artery disease) is the most common form of heart disease. A condition known as atherosclerosis results when fatty material such as cholesterol accumulates on an artery wall forming plaque that obstructs blood flow. When the obstruction occurs in one of the main arteries leading to the heart, the heart
does not receive enough blood and oxygen and its muscle cells begin to die. The primary symptom of this condition is pain in the upper left part of the chest that radiates down the left arm—what is called angina pectoris. A heart attack (myocardial infarction) occurs when blood flow to the heart is completely blocked.
Numerous types of drugs have been developed to treat patients with heart disease. Some drugs are given to make the heart beat more slowly, removing stress placed on it. Other drugs cause blood vessels to dilate or stretch. This also reduces stress on the heart. A third important type of drug reduces cholesterol in the blood.
Surgical procedures are often used to treat heart disease. One procedure is known as coronary bypass surgery. To supply blood to the coronary artery beyond the point of blockage, blood vessels are taken from other parts of the body (often the leg) and connected to the artery. Another commonly performed procedure is angioplasty, during which narrowed arteries are stretched to enable blood to flow more easily. The surgery involves threading a balloon catheter (tube) through the coronary artery and then stretching the artery by inflating the balloon.
The most dramatic treatment for heart disease is the replacement of damaged hearts with healthy human or even animal hearts. The first successful human heart transplant was performed by South African surgeon Christiaan Barnard (1922– ) in 1967. The patient, however, died in 18 days. Many patients who received early heart transplants died days or months after the operation, mostly because their bodies rejected the new organ. In the early 1980s, effective drugs were developed to fight organ rejection. By the late-1990s, the one-year survival rate of patients receiving heart transplants was over 81 percent. For those who survived the first year, survival rates rose to over 90 percent.
[See also Circulatory system; Electrocardiogram; Transplant, surgical ]
heart
heart / härt/ • n. 1. a hollow muscular organ that pumps the blood through the circulatory system by rhythmic contraction and dilation. In vertebrates there may be up to four chambers (as in humans), with two atria and two ventricles. ∎ the region of the chest above the heart: holding hand on heart for the Pledge of Allegiance. ∎ the heart regarded as the center of a person's thoughts and emotions, esp. love or compassion: hardening his heart, he ignored her entreaties he poured out his heart to me | he has no heart. ∎ one's mood or feeling: they had a change of heart. ∎ courage or enthusiasm: they may lose heart as the work mounts up Mary took heart from the encouragement handed out I put my heart and soul into it and then got fired.2. the central or innermost part of something: right in the heart of the city. ∎ the vital part or essence: the heart of the matter. ∎ the close compact head of a cabbage or lettuce.3. a conventional representation of a heart with two equal curves meeting at a point at the bottom and a cusp at the top. ∎ (hearts) one of the four suits in a conventional pack of playing cards, denoted by a red figure of such a shape. ∎ a card of this suit. ∎ (hearts) a card game similar to whist, in which players attempt to avoid taking tricks containing a card of this suit.4. the condition of agricultural land as regards fertility.PHRASES: after one's own heart of the type that one likes or understands best; sharing one's tastes: a man after God’s own heart.at heart in one's real nature, in contrast to how one may appear: he's a good guy at heart.break someone's heart overwhelm someone with sadness.by heart from memory.close (or dear) to (or near) one's heart of deep interest and concern to one.from the (bottom of one's) heart with sincere feeling: their warmth and hospitality is right from the heart.give (or lose) one's heart to fall in love with.have a heart [often in imper.] be merciful; show pity.have a heart of gold have a generous nature.have the heart to do something be insensitive or hard-hearted enough to do something: I don't have the heart to tell her.have (or put) one's heart in be (or become) keenly involved in or committed to (an enterprise).have one's heart in one's mouth be greatly alarmed or apprehensive.have one's heart in the right place be sincere or well intentioned.heart of stone a stern or cruel nature.hearts and flowers used in allusion to extreme sentimentality.hearts and minds used in reference to emotional and intellectual support or commitment: a campaign to win the hearts and minds of America's college students.one's heart's desire a person or thing that one greatly wishes for.one's heartstrings used in reference to one's deepest feelings of love or compassion: the kitten's pitiful little squeak tugged at her heartstrings.in one's heart of hearts in one's inmost feelings.take something to heart take criticism seriously and be affected or upset by it.wear one's heart on one's sleeve make one's feelings apparent.with all one's heart (or one's whole heart) sincerely; completely.with one's heart in one's boots in a state of great depression or trepidation: I had to follow her with my heart in my boots.DERIVATIVES: heart·ed adj. [in comb.] a generous-hearted woman. ORIGIN: Old English heorte, of Germanic origin; related to Dutch hart and German Herz, from an Indo-European root shared by Latin cor, cord- and Greek kēr, kardia.
Heart
HEART
HEART (Heb. לֵב, lev, pl. לִבּוֹת, libbot; לֵבָב, levav, pl. לְבָבוֹת, levavot). The corresponding Hebrew words only sometimes have the meanings in question but many translators and writers on Bible are, or act as if they were, largely unaware of the fact.
strictly anatomical senses of lev and levav
Senses That Do Not Include the Heart
breast
The current English translations reveal an awareness that in Nahum 2:8 [7] levav means not heart but breast and rightly represent the women as "beating their breasts"; but breast is no less certainly the meaning of lev in Exodus 28:29–30 (three times in all). Again, in ii Samuel 18:14–15, since it is only the attack of 10 of Joab's henchmen that finishes Absalom off after their leader has stuck three darts into the victim's lev, those darts must have been stuck, not into his heart, but into his breast. Somewhat similar is the case of ii Kings 9:23–24. Jehoram is trying to flee from Jehu in his chariot, but an arrow from Jehu's bow overtakes him and strikes him "between the arms." Now, the rendering of some recent Bible translations (most recently neb), "between the shoulders," is perhaps too free, but it is historically correct, since it can be seen on contemporary Assyrian reliefs that the lowness of the chariot floor compelled the charioteer to extend his arms horizontally when, like Jehoram here (verse 23), he held the reins in his hands. Add to this that the ground was level (Jezreel), and Jehu only a short distance behind Jehoram, and one must wonder what view of the course of the arrow through the hapless Omrid's chest was adopted by the same translators to account for the statement that "the arrow pierced his heart." What the words va-yeẓe (wa-yeẓeʾ) ha-ḥeẓi mi-libbo do mean is – word for word – "and the arrow emerged from his breast." Probably Jeremiah 17:1 is still another instance. This sense of lev, by the way, is not confined to biblical Hebrew (see Sot. 1:5; Mak. 3:12). The word ḥazeh ("breast"), unlike its Aramaic etymon, seems to have been used only of animals so long as Hebrew was a living language.
throat
This is what lev means in Isaiah 33:18; Psalms 19:15; 49:4; Job 8:10; Ecclesiastes 5:1. Lev is either parallel to peh ("mouth") or associated with the root hgy (which always denotes audible sounds, including the coo of the dove (Isa. 38:14; 59:11), the growl of the lion (Isa. 31:4), and the twang of the lyre (Ps. 92:4), and never silent meditation), or both, with the exception of Job 8:10, in which lev alternates with the peh of the otherwise identical phrase in 15:13. In fact, lev is the proper word for "throat" in biblical Hebrew, garon taking its place only where the former would be misunderstood (as where loʾ yehgu be-libbam would have meant not, "They cannot utter sounds with their throats," but "They do not speak sincerely," see Hos. 7:14).
Senses that Include the Heart
Even where the word lev clearly refers to something inside the body cavity, it does not always mean specifically the heart. It doubtless does when it is paired with "kidneys" (Jer. 11:20; 17:10; Ps. 7:10; 73:21), but probably more often it merely conveys the general idea of "the insides, the interior of the body"; and from this sense derives its use with yam(mim) ("sea(s)") and ha-shamayim ("the air" or "space") to express the notions "(far) out at sea" and "(high) up in the air (in space)" (Ex. 15:8; Ezek. 27:4, 25–27; 28:2, 8; Ps. 46:3; Prov. 23:34).
not strictly anatomical senses of lev and levav
The interior of the body is conceived of as the seat of the inner life, of feeling and thought. Strong feeling is conceived of as a stirring or heating of the intestines (meʿayim) – Isaiah 16:11; Jeremiah 4:19 [20]; Lamentations 1:20 – as well as of the heart – Deuteronomy 19:6; Jeremiah 48:36; Psalms 39:4. Gladness is a function not only of the heart (e.g., Prov. 23:15) but also of the kidneys (Prov. 23:16; cf. Jer. 12:2b), which also urge a certain course on a man. But it is the lev(av) that figures most often in references to the inner life, both emotional and – and this is its special sphere – intellectual. That is why when lev(av) is mentioned alone it is often hard to decide whether the underlying physical concept is specifically the heart or the inwards generally. At any rate, the Bible never mentions about the lev(av) anything that is literally physical, such as a heartbeat; nor does it ever mention any literal pain or ailment of it. That somebody's "heart" is sick means that he is grieving; that Israel's "heart" is obstructed (older translations, regrettably, "uncircumcised") signifies that it is religiously stubborn and intractable – cutting away the obstruction of Israel's "heart" of course means making it religiously reasonable. So, too, that a man says something "in his heart" means that he says it to himself, or thinks it; that he is "wise of heart" means that he is intelligent or skillful. One who has no "heart" is a dolt. A faithful English translation is precisely one that in most cases does not contain the word "heart," but either substitutes "mind," or sometimes "spirit," or – quite often – does not render the noun at all; for it is often hard to feel, let alone express, the differences between such pairs as "gladness of 'heart'" and plain "gladness," "he rejoiced 'in his heart'" and the bare "he rejoiced," etc. On the other hand, in the interests of both aesthetics and usefulness, "heart" should be substituted in English for the emotional kidneys and intestines of biblical Hebrew: the King James "my bowels were moved for him" (Song 5:4) is not either more beautiful or more enlightening than something like "my heart yearned for him." Finally, on the one hand the word levav illustrates biblical Hebrew's lack of a terminology for distinguishing clearly between mind (or "soul") and body; for when Psalms 104:15 says that bread fortifies a man's levav while wine cheers a man's levav, the first levav means "insides" if not actually "body," but the second one means "spirit." Nevertheless, the words lev and levav enable the language to come close to distinguishing between the two, the former by juxtaposition with basar (בָּשָׂר) the latter by juxtaposition with she'er (שְׁאֵר), two words meaning "body" (lit. "flesh"; see Ps. 73:26; 84:3; Eccles 2:3; 11:10). Psalms 73:26 helps us to detect the fact that the word רֹאשׁ (roʾsh; "head") in Isaiah 1:5 is a corruption, due to contamination by the roʾsh in the following verse, of an original sheʾer, the restoration of which yields for Isaiah 1:5b the sense, "Every body (not just the head but the entire body, see verse 6) is sore and every spirit is anguished."
[Harold Louis Ginsberg]
in the talmud and aggadah
The rabbis adopted the biblical view that the heart is the seat of the emotions, and they applied this notion to every sphere of human action and thought. It is doubtful if they were aware of the circulation of the blood and the part played in this by the heart, but they did state that "all the organs of the body are dependent on the heart" (tj, Ter. 8:10, 46b). In the list of ailments and maladies which render an animal terefah – defects from which they cannot recover – is the perforation of the heart (Ḥul. 3:1).
However, most of the references to the heart in talmudic literature belong to the sphere of ethics. When each of the five disciples of *Johanan b. Zakkai was asked to express his view on "the good way to which a man should cleave and the evil way which he should shun," Johanan gave his approval to the answers of R. Eleazer b. Arakh, "a good heart" and an "evil heart," since "the answers of all the others are included in his" (Avot 2:9). The heart is the seat of all emotions, both good and bad, and commenting on the fact that the longer form levav is used in Deuteronomy 6:5 "thou shalt love the Lord thy God with all thy heart," the Talmud emphasizes that even the evil inclination can be impressed into the service of God, "with both thy inclinations" (the good and the bad; Ber. 54a). The frequently quoted statement, "the All Merciful requires [only] the heart" is not found in that form in the Talmud, but is stated by Rashi (to Sanh. 106b) on the basis of an assertion of similar content.
Prayer is referred to as "the service of the heart" (tj, Ber. 4:1, 7a). The word *kavvanah ("intention," "direction") is found in its fuller and in its verbal form as "the direction of the heart." Thus a person who in the course of reading reaches the *Shema at the time for the obligatory reading of that passage as part of the liturgy: "If he directed his heart he had fulfilled [this obligation]" (Ber. 2:1). The *etrog, which is regarded as the fruit of perfection, is compared on the basis of its shape to the heart (Lev. R. 30:14). The hypocrite is described as he who is "one thing in the mouth and another in the heart" (bm 49a). On the verse "I communed with my own heart" (Eccles. 1:16) the Midrash (Eccles. R. 1:16) enumerates over 60 emotions of the heart, "the heart sees, hears, speaks, falls, stands, rejoices, weeps, comforts, sorrows, can be arrogant, can be broken, etc.," each one demonstrated by an appropriate verse from Scripture.
For the halakhic problems connected with heart transplants, see *Transplants.
[Louis Isaac Rabinowitz]
bibliography:
Y.S. Licht, in: em, 4 (1962), 411–5 (incl. bibl.); H.L. Ginsberg, in: vt, supplement, 16 (1967), 80.