Many studies have demonstrated that coronary artery bypass surgery combined with medical therapy produces a greater degree of improvement in the symptomatic state and in the functional class of the patients with severe coronary artery disease than does medical therapy alone. This can be objectively documented by an improvement in the exercise capacity and by an increase in heart rate and blood pressure attained at the higher level of exercise. The improvement is the result of relief of exercise-induced (and resting) myocardial ischemia documented by increases in heart rate and blood pressure, greater lactate extraction across the myocardium, improvement in left ventricular dysfunction, abolition of exertional hypotension, and by reversal of exercise-induced and of resting thallium-201 defects. Results of coronary bypass surgery performed during 1974-1979 are better than those during 1969-1973.