Giant coronary artery aneurysm with a fistula is a rare condition. We present one of the largest aneurysms of left circumflex coronary artery territory, arising from the left atrial branch of the left circumflex coronary artery. It had a maximum diameter of 10 cm, with a fistulous connection to the right atrium. Total exclusion of the aneurysmal mass was achieved by ligation of the afferent artery, closure of the entry point from within the aneurysm, and closure of the fistulous communication from within the right atrium. The patient’s postoperative course was uneventful.