The major clinical challenge today in the management of patients with stable coronary artery disease is identification of those patients in whom myocardial revascularization would improve or prolong life. Despite widespread use over the past decade, indications for coronary artery bypass grafting remain controversial. A definite need exists for objective measures of the magnitude of myocardial ischemia before operation and for simple assessment of the hemodynamic effects of operation. The close link between myocardial ischemia and dysfunction suggests that measurement of left ventricular function during exercise can be used to assess myocardial ischemia in individual patients. In large patient populations with coronary artery disease (CAD), a relationship has been documented between the anatomic extent of disease and the magnitude of functional alteration. However, individual variation occurs with some patients with single-vessel stenosis demonstrating greater functional impairment than other patients with involvement of three vessels. The hypothesis that patients with the greatest magnitude of exercise-induced left ventricular dysfunction would profit most from surgery was examined in 857 patients studied by radionuclide angiocardiography and coronary arteriography. These patients were followed for survival and pain relief for up to 4 years after institution of medical or surgical therapy. Patients who demonstrated the greatest amount of exercise-induced left ventricular dysfunction had the most favorable outcome to myocardial revascularization by operation as judged by survival and relief. Successful myocardial revascularization commonly caused no change in resting left ventricular function. However, most patients who underwent myocardial revascularization demonstrated a reversal of left ventricular dysfunction during exercise. Therefore, radionuclide angiocardiography during rest and exercise provides useful assessment of patients before and after coronary artery bypass grafting.