Atrioventricular septum

The atrioventricular septum is a small membranous contact-wall between right atrium and left ventricle, situated dorsal to the base of septal cusp of tricuspid valve.

It is composed primarily of the membranous septum, which is a thin, fibrous structure situated between the right atrium and the left ventricle, and to a lesser extent, between the right and left ventricles. This region is bounded dorsally by the base of the interatrial septum, ventrally by the crest of the interventricular septum, and laterally by the annuli of the tricuspid and mitral valves