A battery-powered device consisting of a hermetically-sealed pulse generator, implanted beneath the skin of the chest in a surgically-created pocket, with a pacing lead in or on one chamber of the heart (right atrium or ventricle). It is intended to generate and conduct electrical impulses to the heart typically when the heart beats too slowly (bradycardia) or has other abnormal rhythms (arrhythmias). It may provide constant electrical stimuli to normalize the heartbeat (fixed-rate) and/or provide a stimulus only when electrical activity within the heart is sensed to be abnormal (demand); it is not intended to provide defibrillation therapy.