BACKGROUND: Substantial bleeding after cardiopulmonary bypass(CPB) complicates postoperative patients care. Recently, antifibrinolytic agents have been used as pharmacologic means of reducing blood loss and tranexamic acid(TA) has been known to have a great efficacy. However, the effective dose of TA is not well established and variable doses of TA have been tried. We compared the hemostatic effectiveness of three commonly recommended doses of TA in patients undergoing CPB. METHODS: With institutional review board approval, 80 patients undergoing valvular replacement were randomly divided into four groups; Group I(GI, n=19) was control group. In group II(GII, n=18) 10 mg/kg of TA was loaded and infused for 10 hours with a rate of 1 mg/kg/hr. In group III(GIII, n=22) 6 g of TA was loaded and 10 g of TA was loaded in group IV(GIV, n=21). Homologous blood was transfused when hematdegrees Crit was lower than 20% during CPB or lower than 25% after CPB. Amount of homologous transfusion(HT) and blood loss(BL) for 24 hours were measured. RESULTS: Ten patients were excluded due to reoperation, abnormal preoperative coagulation profile or incomplete records. There was no statistically significant difference in postoperative BL among 4 groups. However, the amounts of homologous transfusion were significantly lesser in GIII and GIV than in GI and GII. There was no specific complication. CONCLUSION: None of TA regimen did reduce the amount of postoperative BL. However the amount of HT was decreased in patients with loading larger dose of TA. Reduction of HT might be attributed to decrease in intraoperative BL which could not be measured. Therefore loading larger dose of TA may be more effective and convenient than loading and infusion of a small dose of TA.