Under observation were kept 80 patients with signs pointing to the sick sinus syndrome. Most of them suffered from ischemic heart disease, from atherosclerotic cardiosclerosis and acute myocardial infarction. Persistent sinus bradycardia with active and passive heterotopic arrhythmias were recorded in 42 patients. Sino-auricular block of the II and III degrees or asystolia of the atria with ectopic arrhythmias were observed in 37 cases. A number of patients displayed fibrillary bradyarrhythmia, extrasystole with post-extrasystolic depression of the rhythm and other disturbances. The so-called tachycardia-bradycardia syndrome characterized by the presence of tachycardiac arrhythmias occurring against the background of a marked bradycardia was registered in 25 persons. Fifteen patients demonstrated attackes of the Morgagni-Adams-Stokes syndrome, usually associated with lengthy periods of cardiac asystole. The treatment of ectopic arrhythmias in patients with the sick sinus syndrome presents considerable difficulties, but in many of them these disorders could be successfully eliminated by a careful and rigidly controlled application of antiarrhythmic agents (isoptin, ajmalin, pulsnorma, rhythmodan, beta-adrenergical blocking agents). For some patients exhibiting a tendency toward asystole electric stimulation of the heart is indicated.