Acute cardiac tamponade requires urgent diagnosis andtreatment. We report a case of a 43-year-old man whowas receiving warfarin treatment for 8 months followingmitral valve replacement. The patient had complaint ofdyspnea and fatigue for a few days. Cardiac tamponadewas diagnosed, and the INR at that time was 10.4. Urgentpericardiocentesis were undertaken and 1400 ml of pericardialblood was drained. Following surgery the patient’srecovery was uneventful. An intravenous vitamin K injectionand fresh frozen plasma transfusion were administeredto reverse the patient’s over-anticoagulated state.The final pathology revealed chronic inflammation andthere was no malignancy, and no bacteria or mycobacteriumwere seen. Emergency physicians should rememberthat over-anticoagulation with warfarin may contribute tocertain complications, including hemopericardium, andthat strict control of target INR should be the goal for patientswho require continuous warfarin treatment. J ClinExp Invest 2013; 4 (2): 229-233Key words: Hemopericardium, tamponade, oral anticoagulation,warfarin, echocardiography