We underwent 21 cases of orthotopic heart transplantation in the mongrel dogs from May, 1988, to April, 1989. The preoperative hematologic and hemodynamic results were similar to those of the previous reports except glucose and albumin. The exposure of operative field was excellent under the median sternotomy. All the cases died within 48 hours and the mean survival time excluding 4 operative deaths was 11.23*9.36 hours [ulcorner.D., range 0.3-35.5 hours] We speculated the main cause of death was low cardiac output due to the myocardial failure. At autopsy, there was feature of intramyocardial hemorrhage and coagulation necrosis suggesting poor myocardial protection. Now our team is ready to do heart transplantation in man but we need more precise experiences, especially on the immunosuppression and myocardial protection. Recently we continue further experiments with improving results.