From December of 1994 to April of 1995, we, SHUH Department of Pediatric Thoracic and Cardiovascular Surgery, studied effects of aprotinin. 95 patients were randomly divided into two groups : group I (n=47) with aprotinin and group ll (n=48) without aprotinin. Aprotinin was given as one shot injection to cardiopulmonary bypass perfusion solution with dose of 50,000 KIUikg. Laboratory data such as hemoglobin, hematocrit, BUH, creatinine, fibrinogen, electrolyte concentration, aPTT, PT, and AT R was checked preoperatively, 5 minutes after anesthesia, 5 minutes and 35 minutes after CPB circulation, and 5 minutes, 3 hours, and 24 hours after reperfusion. Also, chest-tube drainage, transfused amount of RBC, platelet concentrate, and fresh frozen plasma within first 24 hours postoperatively were checked and analyzed after transition nn body weight demension. Only RBC transfused postoperatively had statistical significance with P value of less than 0.001. Others had no difference statistical wise. Postoperative side effects of aprotinin was not detected weeks after the surgery and there was no reoperated patient due to postoperative bleeding.