Idiopathic enlargement of the right atrium.

A case of aneurysmal enlargement of the right atrium was found accidentally during a routine examination. The patient was asymptomatic and free of palpitations or proven rhythm disturbances. The results of echocardiography, magnetic resonance imaging, and cardiac catheterization excluded cardiac malformation, which could have caused secondary enlargement of the right atrium. A partial pericardial defect as a likely cause of herniation of the right atrium was ruled out by magnetic resonance imaging. In keeping with these results, isolated aneurysmal enlargement of the right atrium was diagnosed.