A 31-year-old male patient, underwent Mustard operation in childhood for complete transposition of the great arteries. He required a sequential (DDD-mode) pacemaker due to a complete symptomatic auriculoventricular block, 25 years after the operation. Wires were inserted through the left cephalic vein and placed in the systemic atrium and ventricle, achieving correct sensing and stimulating thresholds. Atrial rhythm disturbances, specially sinus node dysfunction, are frequent after Mustard's operation and increase through the years following the surgical procedure. Atrioventricular conduction disturbances are rare. Treatment by endocavitary pacemaker implies a correct knowledge of the special anatomy in this congenital disease and its surgical correction.