Persistent left superior vena cava is the most common venous congenital malformation and is usually asymptomatic. Its presence could increase the difficulty for transvenous lead implantation. We report a 71-year-old woman with an idiopathic dilated cardiomyopathy, atrial fibrillation and heart failure that required biventricular resynchronization therapy. During the placement of the device a persistent left superior vena cava was detected. The device was placed without problems and the patient had a satisfactory postoperative evolution.