Seven male patients (age 47-70 years) with congestive idiopathic (n = 4) or ischemic (n = 3) cardiomyopathy of functional class 2 (n = 5) or 3 (n = 2) were investigated. In the control study, cardiac output (Fick principle) and intravascular pressures were measured at rest in the supine position and during three consecutive bicycle exercise levels of increasing severity in the sitting position. One hour later, indoramin (0.09 to 0.17, mean: 0.12 mg/kg) was slowly injected over 10 to 20 min in the supine (n = 3) or sitting (n = 4) position and the same protocol was repeated 15 min later. After drug injection, one patient developed major postural hypotension and exercise data were not collected in this patient; data on six patients are thus presented. At rest, indoramin decreased mean heart rate from 91 to 77 beats/min, arterial blood pressure from 123/69 to 102/61 mm Hg, and mean pulmonary arterial pressure from 26 to 22 mm Hg. The effects of indoramin were similar during the three levels of exercise (analysis of variance). At the highest exercise level, heart rate was unchanged (from 135 to 138 beats/min) and cardiac output was slightly increased (from 8.6 to 9.6 L/min); blood pressure (from 166/87 to 155/78 mm Hg); pulmonary arterial pressure (from 49 to 42 mm Hg); mean capillary wedge pressure (from 31 to 22 mm Hg); systemic vascular resistances (from 1,065 to 863 dynes); and total pulmonary resistances (from 523 to 403 dynes) were all significantly lower after indoramin administration.(ABSTRACT TRUNCATED AT 250 WORDS)