Background: Extracorporeal cardiopulmonary resuscitation (ECPR) is being used increasingly in the emergency and critical care field in Japan. A major complication of ECPR is bleeding; however, the optimal initial heparin dose and activated coagulation time (ACT) remain unknown. The aim of this study was to assess the appropriateness of our initial anticoagulation protocol. Methods: We retrospectively evaluated the initial heparin dose, ACT value, and incidence of bleeding and thrombotic complications in post-cardiopulmonary arrest patients who received a fixed, body weight-unadjusted loading dose of unfractionated heparin (3000 U) prior to veno-arterial extracorporeal membrane oxygenator (ECMO) between February 2011 and November 2013 at Mie University Hospital, Japan. Results: ACT was evaluated within 3 h of initiation of 32 consecutive ECPR patients. The mean heparin dose per body weight was 53.6 U/kg and the mean ACT was 231.3 s. In 17 patients, ACT exceeded 200 s. Three patients experienced fatal bleeding in the chest wall within 24 h of receiving ECMO. The mean heparin dose per kilogram body weight, mean initial ACT, and mean duration of cardiopulmonary resuscitation (CPR) did not statistically differ between the patients who experienced fatal bleeding and those who did not. Conclusions: Fixed-dose heparin of 3000-U bolus resulted in a mean heparin dose per kilogram body weight of 53.6 U/kg and an ACT of 231.3 s and experienced 3 out of 32 fatal bleedings. Further researches are warranted to optimize anticoagulation protocol for ECPR patients. [ABSTRACT FROM AUTHOR]