[The persistence of the left vena cava superior and the absence of the right vena cava superior: the implications in the implantation of a definitive pacemaker].

Persistent left superior vena cava and associated absence of the right superior vena cava is exceedingly rare. The authors present a case, diagnosed when a DDD pacemaker system was being implanted, and point out its rarity, possibility of diagnosis by non invasive methods and technical implications in transvenous electrode implantation.