arrhythmia (ă-rith-miă) n. any deviation from the normal rhythm (sinus rhythm) of the heart. Arrhythmias include ectopic beats, ectopic tachycardias, atrial and ventricular fibrillation, and heart block. sinus a. (SA) a normal variation in the heart rate, which accelerates slightly on inspiration and slows on expiration.

arrhythmia A disturbance in the normal rhythm of the heart, usually caused by reduced blood flow within the heart or a defect in the pacemaker (the sinoatrial node) of the heart.