ABSTRACT
A case of idiopathic enlargement of the right atrium (IERA) is described. A 28-year-old woman was admitted to our hospital because of cardiomegaly and a mass in the right atrium. She had had cardiomegaly for at least 8 years. Echocardiography showed an enlarged right atrium and a large mass. Cardiac catheterization demonstrated normal hemodynamic data. Based on these findings, we diagnosed this case as IERA and the right atrial mass was suspected to be myxoma. At operation, a markedly enlarged right atrium was found. The right atrial wall was paper-thin. Through right atriotomy, a giant round thrombus (5×4×4cm) was found. The tricuspid valve showed a normal configuration. After extirpation of the thrombus, the right atrial wall was excised and plicated. The postoperative course was uneventful. IERA is extremely rare and heart failure and sudden death have been reported. Therefore, symptomatic or complicated cases should be treated surgically.