We studied the clinical and hemodynamic effects of dobutamine infused for 24 hr into 10 patients with acute myocardial infarction (less than 4 days) complicated by left heart failure (pulmonary wedge pressure greater than 15 mm Hg, cardiac index less than 3.0 liters/min/m2). We measured pulmonary arterial pressures, pulmonary wedge pressure, right atrial pressure, and intravascular systemic blood pressures. The thermodilution method was used for determinations of cardiac output, and the electrocardiogram was followed with a computerized arrhythmia monitoring system. After 1 and 3 hr of infusion with the optimal dose (averaging 8 micron/kg/min), there was a very significant increase of cardiac index (29%) and a decrease of pulmonary wedge pressure (37%) with a moderate increase of heart rate (20%) an without significant changes in blood pressure. After 24 hr of dobutamine infusion, much of the improvement in left ventricular function was lost. This may be attributed either to a decrease of drug action or to an unfavorable evolution of the clinical status. We conclude that infusion of dobutamine is an effective, potent, and well-tolerated short-term procedure in the management of left heart failure during the acute stage of myocardial infarction.