Coronary artery aneurysm is a rare disease. It occurs in the epicardial space, mostly along the course of major coronary arteries. Here, we report a case of a giant incidental aneurysm embedded in the basal posterior wall of the left ventricle. A 43-year-old woman was referred to our institution for the evaluation of cardiac palpitations that had been present from the previous 2 months. She reported no medical history (such as Kawasaki's disease or hypertension) or previous operative history. Echocardiogram and subsequent cardiac CT revealed a giant aneurysm in the left ventricle, with a direct fistulous connection to a dilated and tortuous left circumflex artery, which showed direct communication with the straight right coronary artery.