Previous studies have shown poor correlations between exercise tolerance and measurements of left ventricular (LV) function during rest in patients with congestive heart failure (CHF). To further evaluate the determinants of exercise tolerance and their relation to prognosis, we performed rest and exercise hemodynamic measurements and blood pool scintigraphy in 27 patients with CHF. All patients were treated with digitalis and diuretic drugs, but not vasodilator drugs. Exercise capacity was assessed by maximal oxygen consumption (VO2max) during upright bicycle ergometry. Both right ventricular (RV) and LV ejection fractions were measured by radionuclide techniques, and arterial, right atrial and pulmonary artery pressures, cardiac output, and derived hemodynamic indexes were determined. As a group, patients with severely impaired exercise tolerance (group 1, VO2max less than 10 ml/min/kg) had significantly higher rest pulmonary capillary wedge and right atrial pressures (30 +/- 4 vs 23 +/- 6 and 12 +/- 4 vs 7 +/- 2 mm Hg, respectively) than those with a VO2max of 10 to 18 ml/min/kg (group 2). They also had lower LV and RV ejection fractions (16 +/- 4% vs 21 +/- 4% and 19 +/- 12% vs 27 +/- 7%, respectively). However, overlap among individual patients was considerable, and only pulmonary capillary wedge pressure at rest correlated significantly (r = 0.69, p less than 0.001) with VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)