Because of its complex anatomical structure and its position in the heart, the coronary sinus, plays a major role in many diagnostic and therapeutic EP procedures. Anatomy of the coronary sinus is crucial during biventricular pacemaker implantation. Mapping of the coronary sinus is of primary importance during left-sided accessory pathway evaluation and ablation. More recently, the coronary sinus musculature and its connections to left and right atrium and to left ventricle have been identified as playing an important role in various types of supraventricular arrhythmias.