27 patients (8 women, 19 men) aged 39-79 (mean 61) years with acute transmural mycoardial infarction and limitation of left ventricular function were treated in the acute stage for 24-72 (mean 55) hours with intravenous infusions of sodium nitroprusside in concentrations of 10-200 microng/min. Haemodynamic measurements before and 12 hours after onset of treatment showed a significant reduction in mean arterial pressure by 19%, in end-diastolic pressure in the pulmonary artery by 33% and in the total peripheral resistance by 32%, whereas stroke volume and cardiac index rose by 12% and 17%, respectively. The percentage improvement was most marked in those patients most severely affected. The mortality rate of cardiogenic shock was reduced to 25%. In a control group with haemodynamically similar left ventricular failure the mortality rate was 55%. However, the total mortality was nearly unchanged as the number of sudden unexpected deaths after the fourth day rose from 23 to 50%. Further investigations will show how these sudden deaths, mainly due to arrhythmias, can be prevented.