A 55-year-old woman was admitted with complaints of recurrent chest pain for eight days. She had a history of intermittent chest tightness and pain for 5 years. Laboratory test showed increased hypersensitive cardiac troponin I of 0.14 μg/L. The ECG showed ST segment depression in leads V1, V2, V3, and V4. Acute non-ST segment elevation myocardial infarction was diagnosed. Echocardiography revealed a hypoechoic mass (8.9 × 7.0 cm) (asterisk, Panel A, see Supplementary material online, Video S1) in front of the right side of the heart. The right atrium (RA) and right ventricle (RV) were compressed and deformed. A cystic cavity (13 mm wide) can be observed in the mass (arrowhead, Panel B, see Supplementary material online, Video S2), which was connected to the dilated right coronary artery (RCA). Enhanced chest CT showed the obviously enhanced RCA entered into the mass (asterisk, Panels C and D), the distal of which was occlusive and dilated like ‘gallbladder’ (arrowhead, Panel C, D and E). Coronary artery aneurysm (CAA) was suspected. Coronary angiography showed abnormal neoplastic dilatation in the proximal segment of the RCA and complete occlusion in the middle segment (arrowhead, panel F, see Supplementary material online, Video S3). The left coronary artery provided collateral circulation to the RCA (see Supplementary material online, Video S4). The patient underwent resection of the mass. The giant mass was observed between RA and RV (panel G) with numerous thrombi inside (panels H and I). Coronary artery bypass surgery was performed successfully after CAA resection.