Nineteen patients in the acute stage of transmural myocardial infarction were given 20 mg nifedipine orally under haemodynamic control. Two groups were differentiated according to the original left ventricular filling pressure: group 1 pressure less than or equal to 15 mm Hg (n1 = 8), group 2 pressure > 15 mm Hg (n2 = 11). In both groups a significant drop in peripheral resistance and thus arterial mean pressure was found 1-2 hours after ingestion of nifedipine. in the compensated patients in group 1 it led to lowering of the left ventricular stroke-work index with virtually unchanged heart rate and constant cardiac index. The lower initial values for stroke-work index in the decompensated group 2 were not influenced by nifedipine. In the patients of group 2 a small but yet significant lowering of the left ventricular filling pressure was obtained with original values of 22.6 mm Hg on average. Thus the use of nifedipine in the acute phase of myocardial infarction leads to a more economical cardiac action in compensated patients. In decompensated cases the results do not deteriorate, and the tendency to reduction of left ventricular filling pressure may even result in a recompensation of the left ventricle.