We report a case of intraoperative coronary embolism in a 52-year-old male patient undergoing mitral valve replacement. The patient had persistent atrial fibrillation and was treated with oral anticoagulants and, in spite of well controlled anticoagulation, he suffered a transient ischemic attack. No intracardiac thrombus was found by transthoracic echocardiography. Three weeks later open heart surgery was performed. During valve surgery no thrombus was found in the left atrium. When cardiopulmonary bypass was discontinued the heart function rapidly deteriorated and the heart swelled up, became bluish, with left atrial pressure rising to 40 mm Hg. It was noticed that the anterior surface of the left ventricle was not moving. Coronary embolism was considered. Multiple thrombi were found and removed from the left anterior coronary artery. After successful thrombectomy the patient came off the pump easily. Early and late postoperative course were uneventful. Intraoperative coronary embolism should be considered when cardiac function is deteriorating and there is an inability to wean the patient from the pump. Early and correct diagnosis is lifesaving.