Coronary artery aneurysm with coronary arteriovenous fistula is a relatively rare clinical setting. We report a surgical case of a 69-year-old male with a giant coronary artery aneurysm, finding coronary arteriovenous fistula on computed tomography (CT). We performed complete aneurysm excision and coronary artery bypass grafting with the left internal thoracic artery to the posterolateral branch. The fistula was located between the giant aneurysm on the circumflex artery and the coronary vein close to the coronary sinus, closed with aneurysm sac. The postoperative CT found no residual aneurysm and fistula. However, the great cardiac vein was thrombosed, and the impeded venous flow by the thrombus seemed to reduce the left ventricular ejection fraction (LVEF). Four months after the operation, the LVEF improved to the preoperative level.