We report the ablation procedure of a concealed accessory pathway (AP) localized within a persistent left superior vena cava (PLSVC) in which the use of the LocaLisa system was of great value. The AP was the source of symptomatic AV re-entrant tachycardia and located in the initial portion of a PLSVC. The LocaLisa system allowed correct catheter placement and monitoring of stability. Five cooled-radiofrequency applications within the PLSVC suppressed the AP. PLSVC is a very unusual site of APs. The use of a navigation system may be extremely helpful in improving catheter ablation placement and stability in a very dilated vessel.