latrogenic thrombosis within the heart is rare following intracardiac operations. We undertook surgery to correct a 30-month-old girl with Fallot's tetralogy. After a period of 6 months following the operation, echocardiography revealed a thrombus measuring 16 by 12 millimetres attached to the tendinous cords supporting the antero-superior leaflet of the tricuspid valve. Medical treatment having failed, we proceeded to surgical excision so as to avoid pulmonary embolisation. Histological examination confirmed the thrombotic nature of the mass.