Pericardial effusion is a common sequel to cardiac surgery. Urgent pericardiocentesis is required in the case of cardiac tamponade. In adult patients, most pericardiocentesis is accomplished using transthoracic echocardiographic imaging. However, transthoracic echocardiographic imaging may interfere with the procedure field in children. We report the case of a 13-month-old boy who developed cardiac tamponade resulting in heart failure after surgical repair of tetralogy of Fallot. Urgent pericardiocentesis was safely performed at the bedside under transesophageal echocardiographic guidance. Transesophageal echocardiographic monitoring during pericardiocentesis in children has the advantages of better imaging of pericardial effusion without procedure-field interference.