The hemodynamic effects of dobutamine were compared with those of digoxin in six patients with cardiac failure within 24 hours of onset of acute myocardial infarction. Dobutamine (8.5 microgram per kilogram of body weight per minute) was given intravenously for 30 minutes and then discontinued until hemodynamics returned toward base line. Digoxin (12.5 microgram per kilogram) was then given intravenously, and hemodynamics were recorded for 90 minutes. Dobutamine decreased left ventricular filling pressure (from 22.3 to 9.8 mm Hg, P < 0.02) and systemic vascular resistance (1686 +/- 188 to 1259 +/- 108 dynes . sec . cm-5), and increased cardiac index (from 2.4 to 3.2 liters per minute per square meter of body-surface area, P < 0.005) and stroke work index (from 24.6 to 36.6 g . m per square meter, P < 0.02), without changing heart rate or arterial pressure. In contrast, digoxin had no effect on filling pressure (18.3 versus 17.0) and only a slight effect on cardiac index (2.2 versus 2.4, P < 0.05) and stroke work index (21.9 versus 27.6, P < 0.05). Thus, dobutamine markedly increased cardiac output, decreased filling pressure, and relieved pulmonary congestion. Digoxin, did not affect preload or afterload.