To determine the effect of aortic valve replacement on reversing abnormalities of left ventricular function in patients with aortic regurgitation, radionuclide cineangiography was used to study 16 sympatomatic patients with aortic regurgitation before and 6 months after aortic valve replacement. Before operation, left ventricular ejection fraction was 46 +/- 3 percent at rest (normal mean +/- standard error of the mean 57 +/- 1 percent; P less than 0.001), and decreased to 37 +/- 4 percent during exercise (normal 71 +/- 2 percent; P less than 0.001). after operation, ejection fraction rose to 58 +/- 4 percent at rest, indistinguishable from the normal value, and during exercise was 53 +/- 4 percent, increased (P less than 0.001) from before operation but significantly (P less than 0.001) subnormal. Thus, aortic valve replacement can improve but usually does not normalize left ventricular function during exercise in symptomatic patients with aortic regurgitation.