This review addresses three aspects of exercise important to the clinical cardiologist, including the therapeutic use of exercise, the adaptations produced by chronic endurance exercise training, and the risks of vigorous exertion. Regular exercise is useful in reducing atherosclerotic coronary heart disease (CHD) risk, treating selected CHD risk factors, managing CHD patients after an initial cardiac event, and in improving effort tolerance in patients with angina pectoris, congestive heart failure, and claudication. Chronic endurance exercise training produces cardiovascular adaptations, including bradyarrhythmias, cardiac enlargement, and cardiac murmurs, which must be differentiated from those conditions that increase the cardiovascular risk of exercise. This risk in young subjects is due to congenital abnormalities and acquired cardiomyopathy, whereas cardiac complications in adults are largely due to atherosclerotic vascular disease. Prevention of exercise-related cardiac events is difficult because of their rarity, and depends on selective preparticipation screening and the careful evaluation of symptomatic athletes before permitting their return to competition...