Heart murmurs

Definition

A heart murmur is an abnormal swishing or whooshing sound made by blood moving through the heart, heart valves, or blood vessels near the heart during the heartbeat cycle. It is heard through a stethoscope by a physician.

Description

When the heart beats, normally it makes two sounds, "lubb" when the valves between the atria and ventricles close, and "dupp" or "dub" when the valves between the ventricles and the major arteries close. A heart murmur is a series of vibratory sounds made by turbulent blood flow through the heart. The sounds are longer than normal heart sounds and can be heard between the normal sounds of the heartbeat.

Heart murmurs can be present at birth or develop later in life. Murmurs are common in infants and children. Nearly two-thirds of heart murmurs in children are produced by a normal, healthy heart and are harmless. This condition is called an innocent heart murmur. It also may be called functional, physiologic, or benign. Innocent heart murmurs are usually very faint, intermittent, and occur in a small area of the chest. They can disappear and reappear from one examination to the next. Most innocent murmurs disappear by adulthood, but some adults may still have them.

Less commonly, heart murmurs can result from a valve defect, narrowed blood vessel, or other cardiovascular defect. These conditions may have been present since birth (congenital) or developed as the result of another medical illness. These conditions, called pathologic heart murmurs, may indicate the presence of a serious heart defect, especially when accompanied by other signs and symptoms of a heart problem such as shortness of breath, rapid heartbeats, or fainting. They are louder, continual, and may be accompanied by a click or gallop sound. Failure to thrive is an accompanying symptom.

Some heart murmurs are continually present; others happen only when the heart is working harder than usual, for example during exercise or with certain illnesses. Heart murmurs can be diastolic, systolic, or continuous. Diastolic murmurs occur during relaxation of the heart between beats, and systolic murmurs occur during contraction of the heart muscle. Continuous murmurs occur during both the relaxation and contraction of the heart. The characteristics of the murmur may suggest specific alterations in the heart or its valves.

Demographics

Heart murmurs are most commonly discovered in children from ages two to four, although they can be diagnosed at any age. Congenital cardiovascular defects that may cause pathologic heart murmurs affect 36,000 infants (about nine of every 1,000 infants or 1 percent of live births) annually in the United States.

Causes and symptoms

Causes

Many children have heart murmurs that are heard by their doctors at some time in their lives. Innocent heart murmurs are caused by blood flowing faster than normal through the chambers and valves of the heart or the blood vessels near the heart. An increased amount of blood flowing through the heart can also cause an innocent heart murmur. Innocent murmurs may be heard in children because their hearts are very close to their chest walls. Sometimes anxiety , stress, fever , anemia, and overactive thyroid cause innocent murmurs.

Pathologic heart murmurs are caused by structural abnormalities of the heart. These include defective heart valves, hypertrophic cardiomyopathy (enlarged heart muscle), holes or abnormal openings in the walls of the heart (septal defects), aortic aneurysm, or other congenital heart disease .

Heart valve disease is the most common cause of pathologic heart murmurs. Valves that are narrow, tight, or stiff (valvular stenosis) do not open completely and limit the forward flow of blood through the valve. Valves that do not close properly may cause blood to leak back through the valve (called valve regurgitation). Bacterial endocarditis (an infection of the heart) or rheumatic fever can damage heart valves or other structures of the heart and lead to heart murmurs.

A septal defect or aortic aneurysm can cause heart murmurs. The most common types of septal defects are atrial septal defect , an opening between the two upper heart chambers (atria), and ventricular septal defect, an opening between the two lower heart chambers (ventricles). Some septal defects close on their own; others require surgical treatment to prevent progressive damage to the heart. An aortic aneurysm is an abnormal bulging of part of the aorta that may cause blood to leak through the aortic valve and flow the wrong direction.

Symptoms

The symptoms of heart murmurs differ, depending on the cause of the heart murmur. Innocent heart murmurs and those that do not impair the function of the heart usually do not have symptoms. Murmurs caused by severe abnormalities of a heart valve or another congenital cardiovascular defect may cause feeding problems or failure to grow normally in infants, shortness of breath, dizziness , fainting, chest pain , palpitations or rapid heartbeats, fatigue with exertion or exercise, and lung congestion.

When to call the doctor

The parent or caregiver should call the child's pediatrician if the child has these symptoms or conditions, which could be the sign of an underlying heart problem:

• feeding problems in infants
• poor weight gain
• swelling in the ankles or feet
• swollen abdomen
• poor exercise tolerance
• recurrent chest colds and respiratory infections
• abnormal blood pressure
• signs of infection including sore throat , general body aches or fever

The parent or caregiver should seek emergency treatment by calling 911 in most areas when the child has these symptoms or conditions:

• bluish skin tone
• bluish coloration around the lips, fingernail beds, and tongue
• breathing difficulties or rapid breathing
• dizziness or fainting
• uncontrolled coughing or coughing with blood
• irregular heart beats or palpitations (abnormal heart beats that feel like fluttering in the chest)
• chest pain (although rare in children)

Diagnosis

Heart murmurs can be heard when a physician listens to the heart through a stethoscope during a regular physical exam or check-up. While listening to the heartbeat, the physician carefully evaluates several factors, including the loudness, frequency, pitch, duration, location, and timing of the murmur with the patient's heartbeat. A systolic heart murmur may be classified according to how loud it is, based on a scale from one to six, with a grade 6 being the loudest. However, this scale is not a precise measurement, since it is based on each physician's judgment. If a suspicious heart sound is detected, the physician will evaluate how breathing, exercise, or change of body position affect the sound.

Murmurs caused by congenital cardiovascular disease are often heard at birth or during infancy.

Very loud heart murmurs and those with clicks or extra heart sounds should be evaluated further. Infants who have heart murmurs and do not thrive, eat, or breathe properly, and older children who lose consciousness suddenly or are intolerant to exercise should be evaluated. Children with these symptoms may be referred to a pediatric heart specialist, called a pediatric cardiologist. The cardiologist will perform a physical examination, review the child's personal and family medical history, and order tests to evaluate the source of the heart murmur.

The physical exam will be performed to identify signs of illness or physical problems. The child's blood pressure, pulse, reflexes, and height and weight are measured and recorded. Internal organs are palpated, or felt from the outside, to determine if they are enlarged.

To determine if the child has any conditions or disorders that might increase the risk of a cardiovascular defect, the physician will review the child's family medical history.

Tests may include a chest x ray, echocardiogram, or electrocardiogram. A chest x ray is used to look at the size, shape, and location of the heart and lungs. The chest x ray can indicate if the heart is enlarged and can help the doctor identify some heart and lung problems.

An echocardiogram, or echo (cardiac ultrasound) may be used to distinguish an innocent murmur from a pathologic one. On the echo, the doctor may be able to identify a structural heart or vascular problem that is causing the heart murmur. An echo uses ultrasound, or high-frequency sound waves, to create an image of the heart's internal structures. The technician applies gel to a hand-held transducer then presses it against the patient's chest. The sound waves are converted into an image that can be displayed on a monitor. Performed in a cardiology outpatient diagnostic laboratory, the test takes 30 minutes to an hour.

An electrocardiogram (ECG) shows the heart's electrical activity and may reveal muscle thickening, damage, or a lack of oxygen. Electrodes (small, sticky patches) covered with conducting jelly are placed on the patient's chest, arms, and legs. They send impulses of the heart's activity through a monitor (oscilloscope) to a recorder that traces them on a moving strip of paper. The test takes about 10 minutes and is commonly performed in a physician's office. An exercise ECG can reveal additional information.

Cardiac magnetic resonance imaging (MRI) is a scanning method that uses magnetic fields and radio waves to create three-dimensional images of the heart. The MRI reveals how blood flows through the heart and how the heart is working. Although not commonly used to diagnose heart murmurs, it may be used to help physicians evaluate certain congenital cardiovascular defects.

In rare cases when the chest x ray, echo, or ECG tests are not conclusive enough to confirm the presence of an underlying congenital cardiovascular defect, a more invasive diagnostic procedure such as angiography and cardiac catheterization may be performed to show the type and severity of heart disease. These procedures should be performed by a specially trained physician and diagnostic team in a well-equipped heart center.

During the catheterization, a long, slender tube called a catheter is inserted into a vein or artery and slowly directed to the heart, using x-ray guidance. To better view the heart and blood vessels, contrast material (dye) is injected through the catheter and viewed and recorded on an x-ray video as it moves through the heart. This imaging technique is called angiography.

Treatment

Innocent heart murmurs do not affect the patient's health and require no treatment. If a septal defect is causing the heart murmurs, corrective surgery may be required. If heart valve disease is causing the heart murmurs, treatment may include medications or surgery. Valve replacement or valve repair surgery are two treatment options for severely damaged or diseased valves. The pediatric cardiologist can recommend the appropriate type and timing of treatment, based on the child's age, condition, and overall health. Patients with heart disease need prophylactic antibiotic for any dental work or medical procedures they undergo.

Alternative treatment

Alternative and complementary therapies include approaches that are considered to be outside the mainstream of traditional health care. If a heart murmur requires surgical treatment, there are no alternative treatments, although there are alternative therapies that are helpful for pre- and post-surgical support of the patient, such as guided imagery for relaxation.

If the heart murmur is innocent, heart activity can be supported using the herb hawthorn (Crataegus laevigata or C. oxyacantha ) or coenzyme Q10. These remedies improve heart contractility and the heart's ability to use oxygen. If the murmur is valvular in origin, herbs that act like antibiotics and build resistance to infection in the valve areas may be considered.

Before using any particular technique or remedy, it is important for the parent/caregiver and child to learn about the therapy, its safety and effectiveness, potential side effects, and the expertise and qualifications of the practitioner, if applicable. Although some practices are beneficial, others may be harmful to certain patients. Alternative treatments should not be used as a substitute for medical therapies prescribed by a doctor. Parents should discuss these alternative treatments with the child's doctor to determine the techniques and remedies that may be beneficial for the child.

Nutritional concerns

Children with an underlying congenital cardiovascular defect tend to gain weight slowly. An 8-ounce to 1-pound (225–450-gram) weight gain in a month may be acceptable. The physician will monitor the child's weight gain and advise the parents of the goal weight gain and any necessary dietary changes. The most common reason for poor growth among children with congenital cardiovascular defects is they are not taking in enough calories or nutrients. Some other factors that may interfere with growth are the following:

• rapid heart beat and increased breathing rate
• poor appetite
• decreased food intake due to rapid breathing and fatigue
• frequent respiratory infections
• poor absorption of nutrients from the digestive tract
• decreased oxygen in the blood

For infants with congenital cardiovascular defects, nutrition supplements may need to be added to regular formula or breast milk. Sometimes additional feedings are required with the aid of a nasogastric tube to provide enough calories and promote weight gain. The nasogastric tube is placed in the baby's nose and passes to the stomach, and formula or breast milk is delivered through the tube. Breastfeeding may not be possible right after delivery, depending on the child's condition, so a breast pump may be used to maintain the mother's milk supply during times when the baby cannot nurse.

KEY TERMS

Anemia —A condition in which there is an abnormally low number of red blood cells in the bloodstream. It may be due to loss of blood, an increase in red blood cell destruction, or a decrease in red blood cell production. Major symptoms are paleness, shortness of breath, unusually fast or strong heart beats, and tiredness.

Artery —A blood vessel that carries blood away from the heart to the cells, tissues, and organs of the body.

Atrial —Referring to the upper chambers of the heart.

Atrial fibrillation —A type of heart arrhythmia in which the upper chamber of the heart quivers instead of pumping in an organized way. In this condition, the upper chambers (atria) of the heart do not completely empty when the heart beats, which can allow blood clots to form.

Bacterial endocarditis —An infection caused by bacteria that enter the bloodstream and settle in the heart lining, a heart valve, or a blood vessel. People with congenital cardiovascular defects have an increased risk of developing bacterial endocarditis, so preventive antibiotics are prescribed before surgery, invasive tests or procedures, and dental work to reduce this risk.

Congenital —Present at birth.

Echocardiogram —A record of the internal structures of the heart obtained from beams of ultrasonic waves directed through the wall of the chest.

Electrocardiagram (ECG, EKG) —A record of the electrical activity of the heart, with each wave being labeled as P, Q, R, S, and T waves. It is often used in the diagnosis of cases of abnormal cardiac rhythm and myocardial damage.

Hypertension —Abnormally high arterial blood pressure, which if left untreated can lead to heart disease and stroke.

Hypothyroidism —A disorder in which the thyroid gland produces too little thyroid hormone causing a decrease in the rate of metabolism with associated effects on the reproductive system. Symptoms include fatigue, difficulty swallowing, mood swings, hoarse voice, sensitivity to cold, forgetfulness, and dry/coarse skin and hair.

Pathologic —Characterized by disease or by the structural and functional changes due to disease.

Pericardium —The thin, sac-like membrane that surrounds the heart and the roots of the great vessels. It has two layers: the inner, serous (or visceral) pericardium and the outer, fibrous (or parietal) pericardium.

Phenylketonuria —A condition caused by a genetic error of the body's metabolism, characterized by the absence of phenylalanine hydroxylase (an enzyme that converts phenylalanine into tyrosine). Phenylalanine accumulates in blood and seriously impairs early neuronal development. The defect can be effectively controlled by diet.

Rheumatic fever —An illness that arises as a complication of an untreated or inadequately treated streptococcal infection of the throat. It ususally occurs among school-aged children and cause serious damage to the heart valves.

Septal —Relating to the septum, the thin muscle wall dividing the right and left sides of the heart. Holes in the septum are called septal defects.

Septum —A wall or partition. Often refers to the muscular wall dividing the left and right heart chambers or the partition in the nose that separates the two nostrils. Also refers to an abnormal fold of tissue down that center of the uterus that can cause infertility.

Stenosis —A condition in which an opening or passageway in the body is narrowed or constricted.

Ventricles —The lower pumping chambers of the heart. The ventricles push blood to the lungs and the rest of the body.

Babies with congenital cardiovascular defects tire quickly during feedings, so frequent feedings are necessary. Feedings should be on-demand and may need to be as frequent as every two hours in the first few months. Some babies have difficulty feeding from a regular bottle nipple, so different brands may need to be tried. If medications are prescribed, they should be given before a feeding. Medications should not be mixed in the formula or breast milk unless the doctor advises to do so.

The pediatrician will advise when solid foods can be started, usually around six months of age. Fat should not be restricted in the diet, especially in the first two years. High-calorie foods and snacks can play an important role in providing good nutrition and helping the child grow at a healthy rate.

Follow-up care

Along with routine medical care and standard immunizations, periodic heart check-ups are necessary in children who have congenital cardiovascular defects. Usually, heart check-up appointments are scheduled more frequently just after the diagnosis or after treatment. Additional immunizations, such as the influenza vaccine, may be recommended.

Prognosis

Most children with innocent heart murmurs grow out of them by the time they reach adulthood. Children with complex heart disease may continue to need special medical attention throughout adolescence and into adulthood for survival and to maintain quality of life.

Prevention

Heart murmurs cannot be prevented. However, if a child has been diagnosed with valve disease or another congenital cardiovascular defect, the American Heart Association recommends regular dental check-ups to prevent infections of the mouth as well as the preventive use of antibiotics to reduce the risk of heart infections (endocarditis). Preventive antibiotics should be taken before surgery, invasive tests or procedures, and dental work.

Parental concerns

It is reassuring to know that two-thirds of heart murmurs are produced by a normal heart and do not require treatment.

If an underlying congenital cardiovascular defect is diagnosed, there are many treatment options that allow children to be fully active and grow up to be healthy adults. If treatment is needed, there is help available to cover medical expenses. Parents can discuss financial aid with the child's doctor or hospital, and some organizations, including the Heart of a Child Foundation and Little Hearts on the Mend Fund, provide financial assistance to children in need of heart surgery. Support groups are available to help parents and caregivers cope with the challenges of providing care for a child with a congenital cardiovascular defect. It is important for parents to take care of themselves, too, by eating properly, exercising regularly, taking care of personal hygiene, keeping in contact with friends and family members for support, and managing stress by practicing relaxation techniques.

So that the proper treatment can be provided in the event of an emergency, children with congenital cardiovascular defects should wear a medical identification bracelet or necklace to alert healthcare providers of their condition.

See also Congenital heart disease.

Resources

BOOKS

Friedman, William F., and John S. Child. "Disorders of the Cardiovascular System." In Harrison's Principles of Internal Medicine. Edited by Dennis L. Kasper, et al. New York: McGraw Hill, 2004.

"If Your Child Has a Congenital Heart Defect." In Heart Diseases and Disorders Sourcebook, 2nd ed. Edited by Karen Bellenir and Peter D. Dresser. Detroit, MI: Omnigraphics, Inc., 2000.

McGoon, Michael D., and Bernard J. Gersh, eds. Mayo Clinic Heart Book: The Ultimate Guide to Heart Health, 2nd ed. New York: William Morrow and Co. Inc., 2000.

Parker, James N., et al. Heart Murmur: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. Boulder, CO: netLibrary, 2004.

Shelov, Stephen P., et al. "Heart Murmurs." In Caring for Your Baby and Young Child: Birth to Age 5, 4th ed. New York: Bantam, 2004.

Topol, Eric J. "Pediatric and Congenital Heart Diseases." In Cleveland Clinic Heart Book: The Definitive Guide for the Entire Family from the Nation's Leading Heart Center. New York: Hyperion, 2000.

Trout, Darrell, and Ellen Welch. Surviving with Heart: Taking Charge of Your Heart Care. Golden, CO: Fulcrum Publishing, 2002.

Wild, C. L., and M. J. Neary. Heart Defects in Children: What Every Parent Should Know. Minneapolis, MN: Chronimed Publishing, 2000.

ORGANIZATIONS

Adult Congenital Heart Association (ACHA). 1500 Sunday Dr., Suite 102, Raleigh NC 27607–5151. Web site: <www.achaheart.org>.

American College of Cardiology. Heart House, 9111 Old Georgetown Rd., Bethesda, MD 20814–1699. Web site: <www.acc.org>.

American Heart Association. 7320 Greenville Ave., Dallas, TX 75231–4596. <www.americanheart.org/children>.

Children's Heart Services. PO Box 8275, Bartlett, IL 60108–8275. Web site: <www.childrensheartservices.org>.

The Cleveland Clinic Heart Center. The Cleveland Clinic Foundation, 9500 Euclid Ave., F25, Cleveland, Ohio, 44195. Web site: <www.clevelandclinic.org/heartcenter>.

Congenital Heart Disease Information and Resources. 1561 Clark Dr., Yardley, PA 19067. Web site: <www.tchin.org>.

Heart Support of America. 4873 N. Broadway, Knoxville, TN 37918. Web site: <www.heartsupport.com>.

International Children's Heart Foundation. 1750 Madison, Suite 100, Memphis, TN 38104. Web site: <www.babyhearts.com>.

National Heart, Lung, and Blood Institute. PO Box 30105, Bethesda, MD 20824–0105. Web site: <www.nhlbi.nih.gov>.

Texas Heart Institute. Heart Information Service, PO Box 20345, Houston, TX 77225–0345. Web site: <www.tmc.edu/thi>.

WEB SITES

"The Heart: An Online Exploration." Franklin Institute Online. Available online at <http://sln2.fi.edu/biosci/heart.html> (accessed November 19, 2004).

HeartCenterOnline. Available online at <www.heartcenteronline.com> (accessed November 19, 2004).

Heart Information Network. Available online at <www.heartinfo.org> (accessed November 19, 2004).

OTHER

The Heart of a Child Foundation. Financial assistance to children in need of heart surgery. 26710 Fond Du Lac Rd., Rancho Palos Verdes, CA 90275. Web site: <www.heartofachild.org> (accessed November 19, 2004).

Little Hearts on the Mend Fund. Financial assistance to children in need of heart surgery. Available online at <www.littleheartsonthemend.org> (accessed November 19, 2004).

Mended Little Hearts. Support program for parents of children with cardiovascular defects. Available online at <www.mendedhearts.org/MLH/mlh.htm> (accessed November 19, 2004).

Lori De Milto Angela M. Costello

Heart Murmurs

Definition

A heart murmur is an abnormal, extra sound during the heartbeat cycle made by blood moving through the heart and its valves. It is detected by the physician's examination using a stethoscope.

Description

A heart which is beating normal makes two sounds, "lubb" when the valves between the atria and ventricles close, and "dupp" when the valves between the ventricles and the major arteries close. A heart murmur is a series of vibratory sounds made by turbulent blood flow. The sounds are longer than normal heart sounds and can be heard between the normal sounds of the heart.

Heart murmurs are common in children and can also result from heart or valve defects. Nearly two thirds of heart murmurs in children are produced by a normal heart and are harmless. This type of heart murmur is usually called an "innocent" heart murmur. It can also be called "functional" or "physiologic." Innocent heart murmurs are usually very faint, intermittent, and occur in a small area of the chest. Pathologic heart murmurs may indicate the presence of a serious heart defect. They are louder, continual, and may be accompanied by a click or gallop.

Some heart murmurs are continually present; others happen only when the heart is working harder than usual, including during exercise or certain types of illness. Heart murmurs can be diastolic or systolic. Those which occur during relaxation of the heart between beats are called diastolic murmurs. Those which occur during contraction of the heart muscle are called systolic murmurs. The characteristics of the murmur may suggest specific alterations in the heart or its valves.

Causes and symptoms

Innocent heart murmurs are caused by blood flowing through the chambers and valves of the heart or the blood vessels near the heart. Sometimes anxiety, stress, fever, anemia, overactive thyroid, and pregnancy will cause innocent murmurs that can be heard by a physician using a stethoscope. Pathologic heart murmurs, however, are caused by structural abnormalities of the heart. These include defective heart valves or holes in the walls of the heart. Valve problems are more common. Valves that do not open completely cause blood to flow through a smaller opening than normal, while those that do not close properly may cause blood to go back through the valve. A hole in the wall between the left and right sides of the heart, called a septal defect, can cause heart murmurs. Some septal defects close on their own; others require surgery to prevent progressive damage to the heart.

The symptoms of heart murmurs differ depending on the cause of the heart murmur. Innocent heart murmurs and those which do not impair the function of the heart have no symptoms. Murmurs that are due to severe abnormalities of a heart valve may cause shortness of breath, dizziness, chest pains, palpitations, and lung congestion.

Diagnosis

Heart murmurs can be heard when a physician listens to the heart through a stethoscope during a regular check-up. Very loud heart murmurs and those with clicks or extra heart sounds should be evaluated further. Infants with heart murmurs who do not thrive, eat, or breath properly and older children who lose consciousness suddenly or are intolerant to exercise should also be evaluated. If the murmur sounds suspicious, the physician may order a chest x ray, an electrocardiogram, and an echocardiogram.

An electrocardiogram (ECG) shows the heart's activity and may reveal muscle thickening, damage, or a lack of oxygen. Electrodes covered with conducting jelly are placed on the patient's chest, arms, and legs. They send impulses of the heart's activity through a monitor (oscilloscope) to a recorder which traces them on paper. The test takes about 10 minutes and is commonly performed in a physician's office. An exercise ECG can reveal additional information.

An echocardiogram (cardiac ultrasound), may be ordered to identify a structural problem that is causing the heart murmur. An echocardiogram uses sound waves to create an image of the heart's chambers and valves. The technician applies gel to a hand-held transducer then presses it against the patient's chest. The sound waves are converted into an image that can be displayed on a monitor. Performed in a cardiology outpatient diagnostic laboratory, the test takes 30 minutes to an hour.

Treatment

Innocent heart murmurs do not affect the patient's health and require no treatment. Heart murmurs due to septal defects may require surgery. Those due to valvular defects may require antibiotics to prevent infection during certain surgical or dental procedures. Severely damaged or diseased valves can be repaired or replaced through surgery.

Alternative treatment

If a heart murmur requires surgical treatment, there are no alternative treatments, although there are alternative therapies that are helpful for pre- and post-surgical support of the patient. If the heart murmur is innocent, heart activity can be supported using the herb hawthorn (Crataegus laevigata or C. oxyacantha ) or coenzyme Q10. These remedies improve heart contractility and the heart's ability to use oxygen. If the murmur is valvular in origin, herbs that act like antibiotics as well as options that build resistance to infection in the valve areas may be considered.

Prognosis

Most children with innocent heart murmurs grow out of them by the time they reach adulthood. Severe causes of heart murmurs may progress to severe symptoms and death.

KEY TERMS

Atria— The upper two chambers of the heart.

Echocardiogram— A non-invasive ultrasound test that shows an image of the inside of the heart. An echocardiogram can be performed to identify any structural problems which cause a heart murmur.

Electrocardiogram— A test that shows the electrical activity of the heart by placing electronic sensors on the patient. This test can be used to confirm the presence of a heart murmur.

Pathologic— Characterized by disease or the structural and functional changes due to disease. Pathologic heart murmurs may indicate a heart defect.

Ventricles— The lower two chambers of the heart.

Resources

ORGANIZATIONS

American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. 〈http://www.americanheart.org〉.

Texas Heart Institute. Heart Information Service. PO Box 20345, Houston, TX 77225-0345. 〈http://www.tmc.edu/thi〉.