Cardiac varix is a rare entity. It is generally small and is in relation to the interatrial septum, often mistaken as cardiac myxoma. A 19-year-old girl, on evaluation of respiratory infection, was found to have a mass compressing the right atrium. Computed tomographic scan and magnetic resonance imaging suggested a differential diagnosis of pericardial cyst or hydatid cyst. Peroperatively, a large (8 x 6.5 x 5.5 cm) cystic lesion in relation to the right atrial free wall was found. The histopathology of the resected mass revealed it to be a cardiac varix. The case is notable for its large size and its location in relation to the right atrial free wall.