The coronary sinus (CS) has been described as a substrate being involved in the atrial fibrillation (AF) process. However, there are no data describing the CS as a single source of AF. We report a patient with paroxysmal AF who demonstrated an arrhythmogenic focus within the proximal CS as single source initiating and driving AF. This discrete spot was characterized by a sharp "pulmonary vein-like" spike potential preceding every beat during AF and following the atrial potential during sinus rhythm. Radiofrequency ablation at that site led to elimination of the spike potential, disappearance and noninducibility of AF.
