A 44-year-old woman was transferred to the authors' institution in cardiogenic shock secondary to a presumed viral myocarditis and subsequently was placed on venoarterial extracorporeal membrane oxygenation. Transthoracic echocardiography revealed a large right atrial mass of unknown etiology and moderate pericardial effusion. The patient was taken to the operating room for surgical removal of the right atrial mass. Intraoperative transesophageal echocardiography demonstrated cardiac tamponade with complete invagination of the right atrium. Surgical evacuation of the pericardial effusion reverted the right atrium, with no further evidence of the right atrial mass, and no mass was discovered after right atriotomy, indicating that the right atrial "mass" was likely the result of complete inversion of the right atrium in the setting of cardiac tamponade.