In patients with aortic regurgitation,, left ventricular dysfunction at rest, which is associated with a poor long-term prognosis, often develops before severe symptoms. To determine whether evidence of left ventricular dysfunction could be detected before it appeared at rest, 43 patients with severe aortic regurgitation were studied using radionuclide cineangiography during exercise. In 30 normal subjects, left ventricular ejection fraction increased during exercise (57 +/- 1 percent [mean +/- standard error] at rest, 71 +/- 2 percent during exercise, P less than 0.001). In contrast, among 21 symptomatic patients, ejection fraction was normal at rest in 14 patients (average 47 +/- 2 percent) but normal during exercise in only one patient (average 38 +/- 2 percent, P less than 0.001). Ejection fraction was normal at rest in 21 of 22 asymptomatic patients (average 62 +/- 2 percent) but was normal during exercise in only 13 (average 57 +/- 3 percent, P less than 0.001). Thus, exericse-induced left ventricular dysfunction can precede symptoms and dysfunction at rest. Radionuclide assessment of left ventricular function during exercise may prove valuable in sequentially following the state of left ventricular function in patients before the onset of symptoms or of irreversible left ventricular failure.