There are patients with cardiac arrhythmias for whom no medication is effective. When these patients undergo a thoracic sympathectomy, where the part of the sympathetic nerve that innervates the heart is removed on both sides of the chest, their symptoms can go away completely. Since the same standardized sympathectomy procedure is used in every patient, no one knows why the surgery works in only some patients and no one can predict based on the type of arrhythmia or clinical symptoms who is the best candidate for this procedure. We have formed a new group of multidisciplinary investigators to investigate our hypothesis that a subset of patients with cardiac arrhythmias have sodium channel mutations in the nerves that innervate the heart that cause sympathetic nerve overactivity and increase their susceptibility to arrhythmias. We seek to understand if sodium ion channel mutations are a way to identify those patients who best respond when treated by bilateral thoracic sympathectomy.