Objective To evaluate the blood-saving effect of different doses of tranexamic acid in patients undergoing cardiac valve replacement with cardiopulmonary bypass (CPB).Methods Ninety ASA physical status l-Ⅲ patients,aged 18-60 yr,with body mass index of 16-25 kg/m2,scheduled for elective cardiac valve replacement with CPB,were equally and randomly divided into 3 groups using a random number table:control group (group C),large-dose tranexamic acid group (group TL) and small-dose tranexamic acid group (group TS).Anesthesia was induced with iv injection of midazolam,sufentanil and pipecuronium.The patients were endotracheally intubated and mechanically ventilated.Anesthesia was maintained with inhalation of isoflurane and iv injection of midazolam,sufentanil and pipecuronium.After induction of anesthesia,tranexamlc acid 20 mg/kg was intravenously infused over 30 min,followed by continuous infusion at 20 mg· kg-1 · h-1 until the end of operation in group TL,tranexamlc acid 10 mg/kg was intravenously infused over 30 min,followed by continuous infusion at 10 mg· kg-1 · h-1 until the end of operation in group TS,while the equal volume of normal saline was given instead in group C.Venous blood samples were taken before induction,at the end of operation and at 24 h after operation for determination of hemoglobin (Hb),hematocrit (Hct),and platelct count (Plt).The volume of chest tube drainage was collected and recorded at 6 and 24 h after operation.The requirement for transfusion of allogeneic red blood cells was also recorded.The development of death and complications during days of hospitalization was recorded.Results Compared with group C,the volume of chest tube drainage was significantly decreased,the requirement for transfusion of allogeneic red blood cells was reduced (P < 0.05),while no significant changes were found in Hb,Hct and Plt at each time point in TL and TS groups (P > 0.05).There was no significant difference in the parameters mentioned above between group TL and group TS (P > 0.05).The development of death and complications during days of hospitalization was not observed in the three groups.Conclusion Small-dose tranexamlc acid is suitable for blood-saving effect in patients undergoing cardiac valve replacement with CPB,that is loading dose of 10 mg/kg and maintenance dose of 10 mg· kg-1· h-1. Key words: Tranexamic acid; Postoperative hemorrhage; Extracorporeal circulation; Heart valve prosthesis implantation