The moderator band is a muscular band of heart tissue found in the right ventricle of the heart. It is well-marked in sheep and some other animals, and frequently extends from the base of the anterior papillary muscle to the ventricular septum.
The moderator band is important because it carries part of the right bundle branch of the AV bundle of the conduction system of the heart to the anterior papillary muscle. This shortcut across the chamber of the ventricle seems to facilitate conduction time, allowing coordinated contraction of the anterior papillary muscle.
From its attachments it was thought to prevent overdistension of the ventricle, and was named the "moderator band".
The moderator band is often used by radiologists and obstetricians to more easily identify the right ventricle in prenatal ultrasound.