The modern lifestyle, including Western-style eating habits, cigarette smoking, and physical inactivity, is among the multiple contributors to development of atherosclerosis and increased risk of coronary heart disease (CHD). Recent epidemiologic evidence strongly suggests that risk of major CHD events can be substantially reduced with an average of 30 to 60 minutes per day of even moderate-intensity dynamic physical activity (PA). Attenuation of a number of atherogenic metabolic and physiologic risk factors appears to play a role. This includes reductions in elevated levels of plasma triglycerides and their lipoprotein carriers and an incerease in plasma levels of high-density lipoprotein (HDL) cholesterol; reduced blood pressure levels and risk of hypertension; and improved cell insulin sensitivity and glucose tolerance, reducing risk of non-insulin-dependent diabetes mellitus. An associated loss of excess weight and fat and an improvement in VO2max levels with exercise contribute to these antiatherogic effects of exercise. Recent research also suggests that resistive exercise may also favorably alter atherogenic risk factors, but this remains to be confirmed. Other possible contributors to reduced risk of CHD by exercise training are reduced myocardial oxygen demands; increased coronary blood supply; improved myocardial function; reduced myocardial susceptibility to serious ventricular arrhythmias; and a reduced tendency for coronary thrombosis. Additional research is required to confirm and better define the dose—response relationships for these beneficial physiologic adaptations.