The intravenous administration of chlorpromazine in 12 patients with acute myocardial infarction and altered pump function was followed by a significant reduction in systemic vascular resistance (28.4%) and an increased cardiac index (23.0%). The drug also produced a significant decline in mean pulmonary capillary wedge pressure (38.2%), while the heart rate and mean stroke work index did not change significantly. Although the mean blood pressure decreased by 18.3%, the transymocardial pressure gradient was not affected. A significant reduction in the major determinants of myocardial oxygen consumption, such as arterial blood pressure and left ventricular wall tension, suggested a decrease in myocardial demand for oxygen. Improvement of left ventricular performance was associated with a sedative effect in most of the patients. Intravenous administration of chlorpromazine proved to be of benefit in patients with moderate to severe congestive heart failure and cardiogenic shock.