We describe 4 cases of congenitally corrected transposition associated with atrioventricular septal defect, diagnosed by echocardiography and angiocardiography. Two had usual atrial arrangement and two had mirror imaged atrial arrangement . All cases were associated with subpulmonary valvar stenosis. All patients presented with cyanosis and were in sinus rhythm. Atrioventricular septal defect with common atrioventricular junction was easily diagnosed on the basis of a common atrioventricular valve permitting interatrial and interventricular communications. All patients had balanced right and left ventricles. The echocardiographic recognition of the ventricles was based on the presence of the moderator band within the morphologically right ventricle, the characteristics of the apical septal trabeculations, and the shape of the ventricles. Angiocardiographic recognition of the ventricles was achieved on the basis of right and left ventriculography. In one case with usual atrial arrangement, we recorded two His bundle potentials, one anteriorly and another posteriorly. Atrial stimulation revealed blocked atrioventricular conduction at the level of the posterior bundle, and normal atrioventricular conduction through the anterior bundle. In both cases with atrial mirror-imagery, only a posterior His bundle potential was found, with normal atrioventricular conduction revealed by atrial stimulation The clinical course with this combination depends on the other lesions present in addition to the common atrioventricular valve. Our electrophysiological studies show that the conduction system in presence of a common atrioventricular valve is as expected for congenitally corrected transposition with two atrioventricular valves.