Forty patients with chronic obstructive pulmonary disease (COPD) underwent right heart and central catheterization at rest and during exercise when not in a state of acute exacerbation. They were divided into 2 groups of different functional gravity: group I: FEV1 less than or equal to 1250 ml, RV/TLC greater than or equal to 55% (24 patients); group II: FEV1 > 1250 ml, RV/TLC < 55% (16 patients). At rest, group I had mean pulmonary artery pressure, pulmonary arteriolar resistance, and arterial PCO2 significantly higher, and arterial PO2 significantly lower, than group II. There was no difference in cardiac index, mean atrial pressure and pulmonary wedge pressure between the two groups. During exercise, mean right atrial and pulmonary wedge pressure increased markedly in group I and showed a significant difference from the values of group II. For pooled data of groups I and II, there was a correlation between FEV1 and mean right atrial pressure under exercise and between arterial PO2 and right atrial pressure under exercise. It is concluded that (1) subdividing patients with COPD, as reported here, determines two different blood gases and pulmonary hemodynamic subsets when taken at rest; (2) during exercise, group I patients have "abnormal" right and left ventricular function; (3) FEV1 and arterial PO2 on physical exertion serves to predict mean right atrial pressure under exercise.