A 73-year-old woman underwent surgery for removal of a large left atrial myxoma diagnosed by transthoracic echocardiogram. At operation a large tumour was removed, and the left atrium and atrial septum closed. Trans-oesophageal echocardiography prior to weaning from cardiopulmonary bypass revealed that a smaller tumour, which had not been detected by visual inspection or palpation, remained within the left atrium. This was removed through the atrial septum, and the operation completed uneventfully. The patient made a full recovery.