Objective:Evaluate the effect of tranexamic acid with different application time on postoperative bleeding,fibrinolytic activity and platelet function in cardiac valve replacement with cardiopulmonary bypass. Methods:Forty-five patients with heart valve disease were randomly divided into three groups. Group TA-1 received 0.5 g tranexamic acid within 15 min at the beginning of cardiopulmonary bypass,followed by continuous infusion of another 0.5 g during cardiopulmonary bypass. Group TA-2 received 1.0 g tranexamic acid after the bypass. Group control received nothing during and after bypass. Cumulative blood loss at 6 h and 24 h,blood transfusion at 24 h,D-dimer level and platelet count at 6 h after surgery were recorded. Results:Postoperative blood loss and transfusion were significantly reduced in group TA-1 and TA-2 when compared with the control group. Group TA-1 has less blood loss at 6 h and 24 h than group TA-2. The blood transfusion was also less in group TA-1 than TA-2,however the difference was not significant. There was a significant increase in plasma D-dimer level at 6 h after surgery. Among the three groups,group TA-1 has the lowest D-dimer level,which is lower in group TA-2 than in the control group. Platelet count at 6 h after surgery was similarly reduced in the TA-2 group and control group,which was significantly less than that of TA-1 group. Conclusion:Tranexamic acid effectively reduces postoperative bleeding and blood transfusion in patients undergoing cardiac valve replacement with cardiopulmonary bypass compared to the control. Continuous application of tranexamic acid during the cardiopulmonary bypass has a better effect than a single dose after bypass on postoperative bleeding,blood transfusion,anti-fibrinolysis and platelet protection.