A new noninvasive procedure for quantitation of cardiac valve regurgitation was evaluated using a combination of first pass and gated equilibrium radionuclide cardiography in 38 subjects with and without cardiac valve disease. Left-sided cardiac catheterization was performed to determine the severity of mitral incompetence and aortic regurgitation semiquantitatively. In healthy subjects and in patients without valve disease, stroke volumes were nearly identical with the two methods and the correlation was high (r = 0.98 [p less than 0.001]). The mean regurgitation fraction was 13% in patients with mild mitral incompetence and 2+ aortic regurgitation, 37% in patients with moderate mitral incompetence and 3+ aortic regurgitation and 57% in patients with severe mitral incompetence and 4+ aortic regurgitation. These findings suggest that combined first pass and gated equilibrium radionuclide cardiography, being insensitive to intracardiac shunts and right-sided valve disorders, constitutes a valid noninvasive technique for quantitation of left-sided cardiac valve regurgitation.