The commonly used term sick sinus syndrome refers to a constellation of disorders of sinus rhythm that includes (1) inappropriate sinus bradycardia, (2) barious forms of sinoatrial block, (3) sinus arrest, (4) tachycardia-bradycardia syndrome, (5) sinoatrial nodal suppression by ectopic beats, and (6) sinoatrial reentry. This group of arrhythmias is very often associated with other manifestations of conduction system disease, such as aytrioventricular, fascicular, and bundle branch block, and suppression of escape rhythms from subsidiary pacemakers.