Fifteen patients with congestive cardiomyopathy (six idiopathic and nine alcoholic) manifested by heart failure (New York Heart Association class III or IV) were randomly assigned to a protocol in which dobutamine (n = 8) or 5% dextrose in water (n = 7) was infused continuously for 72 hr. The dose of dobutamine was titrated to increase cardiac output to twice the baseline values. The patients were evaluated before infusion, shortly after infusion, and 1, 2, and 4 weeks thereafter. Functional class improved in six of eight dobutamine-treated patients but in only two of seven control patients during the 4 week observation period. Maximal exercise time and left ventricular ejection fraction increased significantly above baseline only in the dobutamine group. However, neither dobutamine nor placebo infusion produced significant changes shortly after infusion in heart rate, cardiac index, or total peripheral vascular resistance at rest or during exercise at similar workloads. The group receiving dobutamine did show a reduction in systemic systolic and pulmonary arterial mean and diastolic pressure at rest (123 +/- 5 to 108 +/- 6, 32 +/- 5, to 24 +/- 3, and 26 +/- 4 to 20 +/- 2 mm Hg, respectively). In addition, total body oxygen consumption during similar workloads was lower after dobutamine infusion than before.(ABSTRACT TRUNCATED AT 250 WORDS)