E PSILON-AMINOCAPROIC acid prophylactically may have its clinical usefulness.’ “We believe that the most common cause of bleeding after heart surgery is fibrinolysis.“* Such statements have been made recently and similar ones have been intimated by a number of well-respected researchers in anesthesiology and surgery. The routine use of medications affecting coagulation is at the moment limited to heparin and protamine. Others have supported the use of 1-deamino-8-D-arginine vasopressin (DDAVP) or, in Europe, aprotinin. Is there a magic intravenous substance that will decrease blood loss substantially without any significant side effects? e-Aminocaproic acid (EACA) and tranexamic acid have been suggested. The biology of fibrinolysis must be understood before a judgment can be made on the use of these compounds for all cardiopulmonary bypass (CPB) cases.