The left ventricular ejection fraction (EF) obtained by first pass radionuclide angiocardiography was compared with that determined by contrast angiocardiography in 49 patients. In 35 of the patients a comparison with the EF obtained by M-mode echocardiography was also made. The EF echo was determined in two ways, from the standard cube formula and the regression equation suggested by Teichholz for left ventricular volume calculations. The latter formula gave an average EF closer to the average EF obtained by isotope technique and cineangiography and was therefore used in the comparison study. Measurements of EF by isotope technique and echocardiography correlated well (r = 0.78). The correlation between these two noninvasive methods for EF determination and their cineangiographic counterpart was almost identical (r = 0.72--0.74).