Left ventricular end-diastolic and end-systolic volume, stroke volume, and ejection fraction were determined by biplane angiocardiography and echocardiography in 27 patients suspected of having heart disease. Angiographic volumes were calculated by the area-length method and echocardiographic volumes, from the left ventricular dimension of the echograms. The angiographic minor diameter and the semilength correlated significantly with the echocardiographic left ventricular dimensions in diastole and systole. Left ventricular size over a wide range compared favorably by each technique, with a correlation coefficient of r = 0.97 for end-diastolic volume (range by angiography 80-585 ml, see ± 27.76), r = 0.97 for end-systolic volume (range by angiography 24-485 ml, see ± 23.64), r = 0.83 for total left ventricular stroke volume (range by angiography 35-229 ml, see ± 25.45), and r = 0.80 for left ventricular ejection fraction (range by angiography 0.18-0.70, see ± 0.09). These data indicate that left ventricular dimensions in systole and diastole can be reliably determined and left ventricular chamber size and ejection fraction can be quantitated in man by the noninvasive technique of echocardiography.