Persistent Left Superior Vena Cava (PLSVC) is the most common congenital abnormality of the thoracic venous system, it is usually diagnosed as an unexpected finding during attempts to left-sided venous catheterisation for intracardiac lead placement which can make more challenging and time consuming. Patients with this congenital malformation are at increased risk of developing various cardiac arrhythmias. It affects approximately 0.5 - 2% of individuals with normal heart, and up to 10 % in the presence of an established congenital heart diseases. We present two different challenging cases of persistent left superior vena cava incidentally discovered during device implantation