We present a case history of a patient with angina of effort associated with hypothyroidism on whom was performed successfully an aortocoronary bypass operation. A 59-year old man was admitted because of dull retrosternal chest pain. Examination of thyroid function demonstrated hypofunction of thyroid gland; EMR, -30 % ; T₃<10 ng/dl ; T₄<1 μg/dl; and TSH, 306 μU/ml. Electrocardiogram examined after an exercise tolerance test showed ischemic depression of ST segment in leads I, ll, aVL and V 4-6. Coronary angiogram showed 90 % stenosis in the main trunk of left coronary artery and proximal regions of the left anterior descending branch and circumflex branch. Left ventriculogram showed reduced wall motion of the anterolateral segment; however, neither akinesis nor dyskinesis was seen. Effort angina with hypothyroidism was diagnosed and aorto-coronary bypass operation was recommended. 76 days after commencement of treatment for thyroid hormone deficiency, aorto-coronary bypass grafts were placed on both the anterior descending branch and circumflex branch using major saphenous vein. After the operation, 50μg dailly of L-thyroxine was given intravenously and from the first postoperative day, 75μg daily of thyroxine was given orally. There was no onset of perioperative myocardial infarction and no angina episodes after operation. Postoperative course was uneventful.