The response of the right ventricle to exercise was examined in 19 patients with heart disease by constructing right ventricular function curves and determining the relationship between right ventricular afterload and preload. Simultaneous cardiac output and right heart pressures were measured at rest, during exercise, and 10 minutes after exercise. The patients were divided into two groups: those in whom the mean right atrial pressure did not rise above 7 mm Hg during exercise (group I, nine patients) and those in whom this variable did rise above 7 mm Hg (group II, 10 patients). A normal range for right ventricular function curves was derived from data reported in the literature. All of the patients in group I remained within this normal range during exercise. Half the patients in group II, however, fell outside the normal range during exercise. For all 19 patients, a linear relationship existed between right ventricular preload and afterload during exercise with a correlation between right atrial mean pressure and pulmonary arterial systolic pressure of r = 0.86.