@@ Cardiopulmonary bypass is an integral component of cardiac surgery. Patients undergoing cardiopulmonary bypass surgery who have significant bleeding after cardiac surgery are at risk of increased mortality and morbidity. Protamine sulphate is administered after cardiopulmonary bypass to neutralize the anticoagulant effect of heparin, thereby establishing normal hemostasis after surgery. Hyun and associate[1]described the reappearance of hypocoagulability after adequate neutralization of heparin and coined the phrase "heparin rebound" to describe this phenomenon. Gollub[2] noted that the prolongation of clotting times postoperatively after initial neutralization could be shortened by the administration of additional protamine and concluded that the phenomenon was caused by reappearance of heparin in the circulating blood. The reported incidence of heparin rebound varies widely and has been reported to be as high as 50％[3].The aim of the present study was to determine whether heparin rebound can be eliminated by additional treatment with protamine sulphate for 4 hours postoperatively and whether this protocol can result in the reduction in postoperative bleeding.