A decrease in systolic blood pressure that occurs with treadmill exercise testing may be a sign of reversible ischemic left ventricular dysfunction. To test this hypothesis, we examined retrospectively the postoperative treadmill responses of 37 patients who had exertional hypotension (end exercise systolic blood pressure less than or equal to initial preexercise levels) before coronary arterial bypass grafting. This group of 37 patients was characterized preoperatively by an abnormal exercise electrocardiogram (36 patients), multiple vessel occlusive disease (36 patients) and a normal ejection fraction at rest (32 patients). Postoperative exercise tests showed improvement in hemodynamic and electrocardiographic changes with reversal of exertional hypotension (33 patients), and conversion to a normal exercise electrocardiogram (29 patients). Coronary bypass surgery can be expected to reverse exertional hypotension in patients with symptomatic angina pectoris and evidence of ischemia in the exercise electrocardiogram.