The purpose of the study was to investigate the effect of exogenous phosphocreatine on the infarction size in experimental occlusion of a coronary artery. Experiments were carried out in anesthetized cats, in which the descending branch of the left coronary artery was ligated. Damaged zone was visualized by intravenous administration of fluorescent Thioflavin T dye. Tissue samples were taken from the heart 3, 6 and 72 hours after the ligation. Exogenous phosphocreatine was administered as a bolus injection (200 mg/kg body weight) 5 minutes before the ligation and was followed by continuous infusion for 3-6 hours at the rate of 5 mg/min/kg body weight. Administration of exogenous phosphocreatine remarkably decreased the size of severe and relative ischemia (by 37% and 71%, respectively, after 3 hours, and by 59% and 86%, respectively, after 6 hours). The size of the necrotic zone, determined after 72 hours, was decreased by 63% in the phosphocreatine experiments.