The ability of radionuclide angiocardiography to quantitatively assess regional left ventricular function was studied in 33 patients undergoing biplane left ventricular cineangiography (45 ° right anterior oblique projection, and 60 ° left anterior oblique projection with 25 ° caudocranial angulation), and first pass (30 ° right anterior oblique projection) and multiple gated equilibrium (35 ° to 45 ° left anterior oblique projection with 20 ° to 25 ° caudocranial angulation) left ventricular scintigraphy within 48 hours. End-diastolic and end-systolic silhouettes of contrast angiograms were superimposed, and five segments were defined in each plane by radial lines originating from the end-diastolic center of mass. Segmental angiographic ejection fraction (end-diastolic area - end-systolic area/ end-diastolic area) was calculated for each segment by computerized planimetry. Similar segments were defined in the end-diastolic and end-systolic regions of interest of the first pass and gated left ventricular scintigrams, and the segmental scintigraphic ejection fraction (back-ground-corrected end-diastolic counts - background-corrected end-systolic counts/background-corrected end-diastolic counts) was obtained for each. A good correlation was observed between segmentai angiographic and scintigraphic ejection fraction in the segments corresponding to the anterobasal (r = 0.74), anterolateral (r = 0.70), apical (r = 0.77), diaphragmatic (r = 0.71), distal septal (r = 0.66), posterolateral (r = 0.71) and inferolateral (r = 0.60) left ventricular regions. The poor correlation in the posterobasal (r = 0.39), basal septal (r = -0.02) and superolateral (r = 0.05) segments was probably related to difficulty in defining the aortic valve, overlap of the left atrium and the left ventricle, and inability to visualize the high septum with these scintigraphic techniques. The reproducibility of scintigraphic segmental ejection fraction was studied in 13 patients in whom a second gated scintigram was performed 2 hours after the initial one. Excellent agreement (r = 0.93) was observed for scintigraphic segmental ejection fraction in the distal septal, posterolateral and inferolateral segments. Segmental scintigraphic ejection fraction enables accurate quantitative evaluation of the function of the anterobasal, anterolateral, apical, diaphragmatic, distal septal, posterolateral and inferolateral left ventricular regions with high reproducibility. © 1981.