Whether exercise causes right ventricular ischemia severe enough to depress right ventricular function is still controversial. Therefore, right ventricular function was evaluated in 44 patients with isolated coronary artery disease of either the proximal left anterior descending or right coronary artery during exercise (n = 22) or balloon occlusion during percutaneous transluminal coronary angioplasty (PTCA) (n = 22). Central hemodynamics and right ventricular volumes were determined using a new thermodilution Swan-Ganz catheter. Exercise increased right ventricular end-diastolic volume index [from 89 (66-127) to 101 (70-130) mlm<sup>-2</sup>, p = 0.00005; median (range)] and stroke volume index [from 44 (27-68) to 53 (36-75) mlm<sup>-2</sup>, p = 0.0005]. During PTCA, right ventricular end-diastolic volume index remained unchanged, while stroke volume index decreased from 49 (38-60) to 40 (26-49) ml m<sup>-2</sup> (p = 0.00005). The decrease in right ventricular ejection fraction during exercise from 56 (41-64) to 52% (39-64) reached only borderline significance (p = 0.06) and was significantly (p = 0.02) smaller than during angioplasty [from 53 (44-62) to 41% (25-66; p = 0.0008)]. Right ventricular ejection fraction did not differ between left anterior descending or right coronary artery obstruction and did not depend on right ventricular afterload. In comparison to exercise angioplasty caused a decreased systolic pressure-volume ratio and a leftward shift of the diastolic pressure-volume curve. In conclusion, exercise has only little effect on right ventricular ejection fraction, whereas inadequate oxygen supply during balloon angioplasty induces severe depression of right ventricular function.