A 29-year-old man, with a diagnosis of congenitally corrected transposition (discordant atrioventricular and ventriculoarterial connections) with associated multiple ventricular septal defects, mild pulmonary valvar stenosis and Ebstein's malformation of a stenotic left-sided morphologically tricuspid valve, died after closure of the ventricular septal defect and insertion of a valved homograft conduit between the morphologically left ventricle and the pulmonary trunk. Death occurred because of failure to appreciate the bizarre and rather stenotic anomaly of the morphologically tricuspid valve, in which the anterosuperior leaflet divided the morphologically right ventricle into an inlet portion and a smaller outlet portion. After closure of the ventricular septal defects, this ventricle could no longer support the systemic circulation. We discuss the natural history and the reasons for the erroneous interpretation of the echocardiographic images of the left-sided tricuspid valve.