A study of 102 patients with primary macrofocal myocardial infarction, admitted to hospital within the first 6 hours after the onset of the disease, and experimental evidence obtained in 110 Wistar rats are reported. In a control group of myocardial infarction patients, collagen synthesis was depressed in the presence of the activation of free-radical lipid oxidation and circulatory hypoxia. Piracetam and inosine treatment was associated with the inhibition of free-radical lipid oxidation and a reduction of hypoxia, those being accompanied by increased collagenogenesis and accelerated postinfarction scar formation. Piracetam, as compared to inosine, had a more marked stimulating effect on the development of compensatory myocardial hypertrophy, thus contributing to rapid recovery of cardiac contractility and reducing manifestations of circulatory insufficiency.