The risks and benefits of regular aerobic exercise have been studied extensively. Because of the potential risks, we believe that sedentary persons over age 40 who have cardiac risk factors, as well as patients with coronary artery disease (CAD), should have a complete physical examination and probably an exercise electrocardiogram before starting a vigorous exercise program. In general, however, regular exercise has proven to be extra-ordinarily safe and the theoretical and proven benefits appear to greatly outweigh the risks in most people, including those with CAD, those with severe left ventricular dysfunction, and the elderly.