Using Nitroglycerin (NTG) and Nitroprusside-Sodium (NPN) intravenously we tried to reduce the necrotic area following myocardial infarction by reducing the myocardial O2 consumption. In 12 patients with acute myocardial infarction the effect of NPN was compared to intravenous NTG. In all patients the blood pressure, the pulmonary artery pressure, the pulmonary capillary wedge pressure and the heart rate were continuously monitored; in few patients with cardiac output was measured using a thermodilution device. In some patients with normal blood pressure NPN lowered the blood pressure to such a degree that NPN had to be discontinued before and effect on the pulmonary capillary wedge pressure could be seen. Even in patients with normal blood pressure this effect was not seen with NTG. Intravenous NTG lowered the pulmonary capillary wedge pressure in most patients with only a moderate effect on the blood pressure. We conclude from our results that patients with acute myocardial infarction and normal blood pressure should receive NTG, if a lowering of the pulmonary capillary wedge pressure is desired. When NPN was used in this group of patients a considerable decline of the blood pressure was seen. We think that an elevated pulmonary capillary wedge pressure should be treated with NPN only in patients with an elevated blood pressure.