Using the EKG, we can localize the source of the electrical activity in the heart. This patient's EKG suggested that the premature beats triggering V-fib were originating in his right ventricle and potentially in his moderator band. The moderator band is a muscular structure in the right ventricle that connects the septum to the anterior papillary muscle. The papillary muscle is part of the supporting structure of the tricuspid valve, which is the heart valve between the right atrium and right ventricle. It is thought that the moderator band facilitates the flow of electrical impulses from the conduction system in the septum to the papillary muscle.