This study examined the degree of left ventricular dysfunction during exercise in patients with silent or symptomatic myocardial ischemia. The left ventricular ejection fraction and volume were measured by radionuclide angiography at rest and peak upright exercise in 108 patients with angiographically documented coronary artery disease and normal resting ejection fraction (≥50%). The 26 patients (24%) who had angina during exercise (symptomatic ischemia) had similar severity of coronary artery disease (Gensini score, 26 ± 14 vs. 22 ± 13), exercise heart rate, exercise systolic blood pressure, and exercise end-diastolic volume to patients who did not experience angina during exercise (silent ischemia). As a group, patients with angina had a greater increase in end-systolic volume with exercise (55 ± 41 vs. 26 ± 58%, p<0.01); a greater decrease in ejection fraction (-8 ± 9 vs. -1 ± 10%, p<0.001) and more abnormal response in the systolic blood pressure to end-systolic volume ratio. Patients with severe dysfunction (≥5% decrease in ejection fraction from rest to exercise) were more likely to have symptomatic ischemia than those who had less severe dysfunction (flat ejection fraction response or actual increase) (20 of 49 (41%) vs. 6 of 59 (10%), p<0.001). However, even among the 27 patients with most severe degree of left ventricular dysfunction during exercise (≥10% decrease in ejection fraction) only 44% had symptomatic ischemia (12 of 27). Thus, among patients with coronary artery disease and normal resting left ventricular function, those with symptomatic ischemia have worse left ventricular function during exercise than those with silent ischemia. However, even in the presence of severe ischemia, most patients were asymptomatic.