The methods of cardioplegia used today are not always able to sufficiently protect the hypertrophied heart. The present study investigated if a recovery period of 30 min before the end of ECC improves metabolic recovery of the heart in comparison to a recovery period of 15 min before terminating extracorporeal circulation. A clinical study was performed of patients undergoing aortic valve replacement. In one group reperfusion was performed for 15 min and in the second group for 30 min before the conclusion of extracorporeal circulation. The concentration of high energy phosphates in the left ventricle was determined at the end of the ischemic period, after 15 min and after 30 min of reperfusion. The behavior of the myocardial metabolites of the two groups showed no differences. Creatinephosphate increased continuously in both groups, while adenosine triphosphate and the adenonucleotide pool did not change during the reperfusion period. From our results we conclude that under the conditions given in our study a recovery period of 15 min is sufficient for metabolic recovery and prolongation of reperfusion before termination of extracorporeal circulation do not improve metabolic recovery.