Scintigraphy using continuous infusion of krypton-81m, (81mKr) is a reproducible, noninvasive method for determining right ventricular ejection fraction (RVEF). Radionuclide determinations of RVEF by 81mKr scintigraphy were compared with those by the technetium-99m (99mTc) first-pass technique in 25 patients; the results obtained by both methods correlated well (r = 0.86, p less than 0.005). In 20 additional patients, the RVEF determined by 81mKr was compared with the RVEF as measured by multislice ECG-gated cardiac X-ray computed tomography, and there was good correlation between RVEFs obtained by the two methods (r = 0.76, p less than 0.005). Furthermore, the RVEF by the 81mKr technique and the LVEF by the 99mTc gated blood pool technique were compared with hemodynamic measurements. There was a significant inverse correlation between RVEF and pulmonary artery pressure or total pulmonary resistance. Other determinants of right ventricular systolic function were the presence of proximal right coronary artery disease, reduced left ventricular function and associated tricuspid regurgitation.