The moderator band was studied in 50 autopsy hearts. It was absent in 5 hearts. Its length and width varied widely. In 11, it appeared as a distinct continuation of the septal band. In other hearts it arose from the lower part of the interventricular septum unconnected with the septal band. It terminated in the anterior papillary muscle or free wall of the right ventricle or both. In one heart, it gave rise to a single chorda which replaced the anterior papillary muscle. In another heart the band gave origin to two papillary muscles. The varied nomenclature and possible function of the moderator band are discussed. Its role in fixation of endocardial leads, causation of intraventricular obstruction functional tricuspid incompetence and conduction disturbances are discussed. In addition to the classical moderator band, anterior and posterior vertical moderator bands were seen in 20 hearts. These described for the first time perhaps help to restrict the right ventricular distension.