Right ventricular function was assessed in 24 patients with COPD, at rest and during submaximal exercise, using both technetium-99m (99mTc) blood-pool and krypton-81m (81mKr) equilibrium ventriculography. Technetium-99m right ventricular ejection fraction (RVEF) at rest was lower than 81mKr RVEF (0.39 +/- 0.12 and 0.54 +/- 0.08, respectively; p < 0.001). During submaximal exercise, there was no increase in RVEF using either imaging technique. This observation contrasted with an increase in RVEF in a group of age-comparable normal subjects during modest submaximal exercise. An inability to obtain spatial separation of right heart structures using 99mTc imaging leads to a value for RVEF that is consistently lower than that measured using 81mKr ventriculography. Resting RVEF is well preserved at rest in most patients with COPD. In contrast to normal subjects, many show an inability to augment right ventricular function during exercise that may contribute to the reduced exercise capacity observed in these patients.