The effects of a short period of ventricular fibrillation on myocardial high energy phosphates were assessed in two groups of rats. Group 1 underwent hypothermic crystalloid cardioplegia infusion and aortic cross-clamping. In Group 2, cardioplegia and cross-clamping were preceded by ten seconds of induced ventricular fibrillation. In rat hearts that had undergone ventricular fibrillation, adenosine triphosphate levels averaged only 70% (p less than .0001) and creatine phosphate levels averaged only 60% (p less than .0005) of levels measured following standard cardioplegic arrest without ventricular fibrillation. These findings are of potential importance in both routine cardiac surgical procedures and in organ procurement.