Both retrograde perfusion via the coronary sinus and direct perfusion of the coronary artery during extracorporeal circulation were studied. Following results were obtained. 1) Coronary perfusion associated with extracorporeal circulation under normothermic condition is far better than with hypothermia in maintainance of cardiac physiology. All the experiments are successfully performed in the case of direct perfusion in this series. 2) It is important to keep perfusion pressure at optimal level during perfusion, which is 35 mmHg. in retrograde and 120 mmHg. in direct perfusion, respectively. Perfusion rate should be controlled within these optimal pressure in each case. 3) Blood flow to mycardium is well maintained in direct perfusion than in retrograde perfusion. Maximum circulatory cessation over 50 minutes is secured in the former method compared to less than 20 minutes in the latter. However, direct perfusion is technically difficult in practice and some divice is needed to facilitate its clinical application. It is preferable to choose one of both methods after direct inspection of valvular lesions following preliminary retrograde perfusion.