We report an unusual case of a giant right coronary artery aneurysm, measuring 15 cm in diameter, in a 76-year old woman. The aneurysm was initially identified when the patient was investigated for signs of congestive cardiac failure with a computed tomography scan of her thorax; at this stage, the lesion was misdiagnosed as a large pericardial cyst. The aneurysm was successfully excised at surgery and her heavily diseased right coronary artery was secured with a saphenous vein graft.