A simple, noninvasive radionuclide technique which measures the severity of valvular regurgitation has been developed. The technique compares right and left ventricular stroke volume indices (change in counts between diastole and systole over the left and right ventricles) from 450 LAO gated cardiac blood pool scans. In 14 control subjects, the left-to-right ventricular stroke index ratio was near unity (1.15 ± 0.15 [SD]). In 26 patients with mitral and/or aortic regurgitation it was larger (range 1.36-5.30, mean 2.44). Comparison between the stroke index ratio and qualitative angiographic estimates of regurgitation revealed good agreement (F = 45.5, p < 0.001). Gated cardiac blood pool scans permit noninvasive assessment of the severity of valvular regurgitation.