Radionuclide ventriculography of the right heart was performed in 56 patients within two weeks of cardiac catheterization using a gated first-pass technique. Thirteen patient served as normal controls, and 43 patients had severe aortic or mitral valve disease or both, 35 of whom subsequently underwent valve surgery. Right ventricular ejection fraction (RVEF) and the presence of central venous reflux was determined and related to catheterization findings. In normal patients, RVEF was 60 plus or minus 7 percent (mean plus or minus 1 SD). In patients with valvular disease, the RVEF was below the normal range in only 2/14 (14 per cent) when right ventricular peak systolic pressures were less than 50 mm Hg, compared with 16/29 (55 percent) with an RVEF below normal when right ventricular peak systolic pressures greater than 50 mm Hg (P less than .05). In contrast, there was no relation of right ventricular ejection fraction to ventricular filling pressure in valvular heart disease patients. There was no difference in early postoperative course in patients with normal or reduced ejection fraction. Central venous systolic reflux was not presented in normal patients, but was present in 3/12 (25 percent) and 22/25 (88 percent); P less than 0.1) of patients with right ventricular systolic pressures below and above 55 mm Hg, respectively, including all ten patients with documented tricuspid regurgitation. Radionuclide assessment of right ventricular function in patients with aortic or mitral valve disease or both provides information that cannot be inferred from right-sided pressure measurements.