BACKGROUND Persistent left superior vena cava (PLSVC) is a structural, asymptomatic and infrequent anomaly, present in 0.5% of the general population. Typically the diagnosis reveals itself unexpectedly at the time of pacemaker implantation, when it acquires anatomic relevancy. Several techniques are used for the transvenous approach to enter the central venous circulation; the left subclavian vein has become a common access site for electrode implantation and, occasionally, one can find an anomalous venous structure such as a PLSVC. Placement of electrodes through this anomalous venous structure can prove challenging, if not impossible. The present report tries to explore aspects of transimplantation diagnosis from a practical point of view. It also address the knowledge of anatomy, implant technique and radiographic orientation. METHODS Twenty-six-year-old woman with confirmed Symptomatic Sick Sinus Syndrome variety Sinus Arrest. The diagnosis of PLSVC was discovered unexpectedly at the time of the transvenous approach. The tip for the diagnosis was the "unusually medial" position of the lead, and the venogram showed the venous traject towards the coronary sinus and drainage into the right atrium. An active-fixation screw-in electrode was positioned in the antero-superior margin of the free wall of the right atrium. After 24 months of successful placement of the pacemaker, the patient is asymptomatic. CONCLUSIONS PLSVC is a rare congenital vascular abnormality. Besides its association with congenital anomalies, its most relevant clinical implication is the association with disturbances of cardiac rhythm, impulse formation and conduction. The ontogenetic development of the sinus node, the atrioventricular node, and the His bundle might be heavily influenced by the lack of regression of the left cardinal vein. When isolated, the PLSVC is usually not recognized until left superior approach to the heart is required, when it becomes a relevant anatomic finding. In fact, it can complicate the positioning of left-sided pacemaker and cardioverter-defibrillator leads. In patients with poor handling through the coronary sinus, a right approach is recommended after visualization of a right superior vena cava entering the right atrium by echocardiography or contrast venography since its absence or hypoplasia (which is reported in 10% of the cases with PLSVC) may represent a major obstacle and would suggest an epicardial implantation. CONCLUSIONS Today, the preferred approach for pacemaker lead implantation is via the left subclavian vein and the operator must be aware of this venous anomaly that may technically complicate the electrode positioning. This kowledge may be useful for other medical specialties that require the implant of left sided transvenous subclavian catheters, like in critical care settings, nephrology, onco-hematology, and anesthesiology.