BACKGROUND: Post-CPB bleeding diathesis remains one of main causes of morbidity in open heart operation since it requires significant amount of homologous transfusion. Many approaches have been studied to reduce the amount of postoperative blood loss and blood use. Aprotinin is known to reduce postoperative bleeding. Therefore, hemostatic effects of aprotinin have been searched in open heart surgery. METHODS: Adult patients for open heart opeartion were randomly allocated to two groups, control group and study group. All anesthetic, surgical and bypass techniques were standardized. After induction, 10,000 KIU given for testing and then 2,000,000 KIU of aprotinin was infused for 20~30 minutes before sternotomy, and followed by at rate of 500,000 KIU/hr. Additional 2,000,000 KIU of aprotinin was mixed to pump prime of heart-lung machine. Aprotinin infusion was ended by the time of skin closure. Amount of postoperative bleeding as well as homologous blood requirement were measured. Urine output and serum creatinine were also documented during postoperative period. RESULTS: Postoperative-36hr summation of blood loss differed significantly(1858.4 1182.9 ml vs. 1256.7 688.4 ml, p<0.1). Postoperative homologous blood requirements were also reduced in the requirement of packed RBCs use(3.0 2.5 units vs. 1.0 0.8 units, p<0.01) and of fresh frozen plasma use(6.6 4.4 units vs. 3.9 2.6 units, p<0.05). Postoperative measurement of urine output and serum creatinine showed insignificant difference between groups while remained within normal range. CONCLUSIONS: High-dose aprotinin seems to have beneficial effect in reducing postoperative blood loss and blood use without renal complication.