Coronary artery bypass grafting (CABG) for patients with ischemic heart disease and hypothyroidism contains many controversies, such as a need of preoperative thyroid replacement therapy and the influences on thyroid function and hemodynamics. A 73-year-old man with three vessel disease including left main trunk lesion was admitted for CABG. Primary hypothyroidism was diagnosed after admission because of high CPK value. The CABG was performed safely with preoperative minimal thyroid replacement and his postoperative course was uneventful. We evaluated the change of perioperative thyroid hormones. At the start of the extracorporeal (ECC), values of T3 and free-T3 decreased progressively, but the change was small. On the other hand, values of T4 and free-T4 increased after the start of ECC. It is suggested that CABG for a patient with angina and hypothyroidism can be performed safely with minimal preoperative thyroid replacement therapy.