I ntroduction: The objective of this prospective, double blind, randomized trial is to evaluate the impact of tranexamic acid (TA) administration after cardiac surgery with cardiopulmonary bypass in postoperative bleeding. Materials and Methods: During induction of general anesthesia, patients received a bolus of TA of 10 mg kg-1 plus 50 mg in the CPB priming followed by a continuous infusion of 1 mg kg-1 h-1 until the end of the surgery. Then, patients were randomly allocated into one of two groups: the isotonic saline (IS) group received 10 ml h-1 of isotonic saline and the TA group received an infusion of 1 mg kg- 1 h-1 of TA. Both groups received their infusions for 10 hours. Primary outcome was bleeding during first postoperative day (POD1). Secondary outcomes were blood transfusion (PRBC, platelets) during POD1 and surgical re-exploration. Anesthesiologists and surgeons were blind to patient allocation. A t-test was used to analyze differences in means of continuous variables and z-test for proportions. A p value < 0.05 was considered statistically significant. Multiple regression analysis was performed to find variables able to predict bleeding in the POD1. Results: 273 patients were included, there were 15 lost per group. 125 patients in the TA group and 118 patients in the IS group were analyzed. Both groups were compared in their demographics characteristics, comorbidity and lab tests and no significant differences were found. No statistically significant differences between groups in the primary and secondary outcomes were found. Multiple regression analysis establishes the variable minutes in cardiopulmonary bypass was able to predict bleeding in the POD1. Conclusions: Postoperative infusion of TA does not decrease bleeding, transfusions and re-explorations during the POD1 of cardiac surgery with cardiopulmonary bypass.