A 68-year-old female patient was referred for the evaluation of an incidentally detected asymptomatic cardiac mass. Imaging studies showed a 3.0 x 2.4 cm, well circumscribed, round, cystic mass with a calcified nodule that was attached to the lower rim of the fossa ovalis in the right atrium. Under cardiopulmonary bypass, the right atrium was opened to reveal a well circumscribed, dark bluish, pedunculated mass. Histologically, the specimen was a unilocular cyst lined by flattened endothelium, with peripheral fibrin clots and dystrophic calcification of the wall. Immunohistochemical staining of the lining cells was positive for cluster designation 34, which represents hematopoietic progenitor cell antigen. The final pathologic diagnosis was compatible with varix of the heart, which should be considered for a cystic mass with a calcified nodule located in the right atrium, near the lower rim of the fossa ovalis.