Ethanol ablation of the vein of Marshall (VOM) has become one of the treatments for persistent atrial fibrillation (AF) and mitral-dependent atrial flutter (AFL). The presence of persistent left superior vena cava (PLSVC) poses a challenge to the procedure. We demonstrated a patient with a large PLSVC where a single conventional balloon could not occlude the vein. By adapting interventional cardiology knowledge and tools, a successful ethanol ablation was achieved using a double-balloon occlusion technique. In conclusion, employing proper devices and adapting interventional cardiology knowledge can result in successful VOM ethanol ablation in this tough scenario.