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 percent) and an increased cardiac index (23.0 percent). The drug also produced a significant decline in mean pulmonary capillary wedge pressure (38.2 percent), while the heart rate and mean stroke work index did not change significantly. Although the mean blood pressure decreased by 18.3 percent, the transmyocardial 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.