This case report describes a patient with Graves' disease who underwent heart surgery and we studied changes in thyroid hormone and antithyroid autoantibodies. TBII index of this case, which was high value before surgery, was decreased after surgery for two years, and the patient did not need any antithyroid drug. It is suggested that these changes may be due to cardio-pulmonary bypass and administration of steroids during heart surgery. This case indicates that heart surgery may influence the clinical course of Graves' disease.