We describe the case of a 3-year-old girl who presented with a large, mobile, ball mass in the right atrium on routine transthoracic echocardiography at one year after an intraatrial repair. Considering the risk of pulmonary embolization, emergent surgery was successfully performed to remove the mass, and histopathological examination revealed that it was a ball thrombus with a fibrin clot. (C) 2016 Elsevier Inc. All rights reserved.