Also known as the [septomarginal trabecula], the [moderator band] is part of the conduction system of the heart.
The moderator band is found in the right ventricle of the heart and extends from the the interventricular septum to the base of the anterior papillary muscle. Although always present, it can have interesting anatomical variations, ranging from being double or triple, to being extremely thin or thick. In some cases, it can be confused as one of the trabeculae carnae.
The moderator band, usually clean on its superior aspect, may present with thin bands of tissue that extend towards the anterior wall of the right heart.
It was initially described by Leonardo Da Vinci, and English anatomists called it the "moderator band", because of its location. The initial belief was that the function of this structure was to prevent excessive ballooning of the right ventricle, "moderating" its dilation. Its descriptive name, the "septomarginal trabecula" was coined by Julius Tandler (1869 - 1936).
The moderator band as part of the conduction system of the heart, allows for some of the fibers of the right bundle branch to reach the wall of the right side of the heart. Click on the image for a larger version
Sources:
1. "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain
2. "Gray's Anatomy"38th British Ed. Churchill Livingstone 1995