The authors report two unusual new cases of corrected transposition of the great arteries diagnosed in patients 72 and 80 years of age respectively, presenting with symptoms of cardiac failure of recent onset. Both patients had mild or moderate regurgitation of the systemic atrio-ventricular valve, associated in one case with aortic regurgitation. This association would appear to be fortuitous although already reported in six occasions. The diagnosis was made by echocardiography and confirmed by catheterisation in one case, and by digitised intravenous angiography in the other. These cases are of interest for three reasons: They are very rare: there have been only 20 comparable cases reported in patients over 40 years of age, the eldest being 73. This is probably explained by the high frequency of associated malformations. They illustrate the decisive role of echocardiography in the diagnosis of congenital heart disease, even in the adult. They constitute a "natural experimental model" of a right ventricle submitted to systemic pressures and tend to show that, in the absence of other abnormalities giving rise to an additional pressure or volume overload, the right ventricle is capable of long term adaptation to this situation. These observations indicate a favourable long-term prognosis for children who have undergone "corrective" surgery at atrial level for simple transposition and in whom the right ventricle is required to assume the function of the systemic ventricle for the rest of their life.