Study of the effects of various diseases and therapeutic manipulation of pulmonary vascular resistance on the right ventricle has been restricted by methodologic limitations. The radioactive gas in solution, krypton-81m was used to study the right ventricle and the technique was compared with a technetium-99m method. In 22 subjects, first-pass krypton-81m right ventricular ejection fraction, acquired both in list mode and electrocardiogram-gated frame mode, correlated well (r = 0.81 and 0.86, respectively, p less than 0.01) with that determined by technetium-99m first-pass studies over a broad range of ventricular function. The reproducibility of the technique was excellent (r = 0.84 and 0.95 for each acquisition mode, respectively). Krypton-81m first-pass studies provide accurate and reproducible estimates of right ventricular function. Use of krypton allows multiple measurements, with or without perturbations, over a short period of time.