Papillary mm.

The papillary muscles are located in the ventricles of the heart. They project inwards into the ventricle from the ventricular walls and attach to the cusps of the atrioventricular (mitral and tricuspid) valve leaflets via the chordae tendineae. The papillary muscles contract to prevent inversion or prolapse of these valves.

There are five total papillary muscles in the heart:

• The anterior, posterior, and septal papillary muscles of the right ventricle each attach via chordae tendineae to a leaflet of the tricuspid valve. 

• The anterior and posterior papillary muscles of the left ventricle each attach via chordae tendineae to a leaflet of the mitral valve.

The papillary muscles of both the right and the left ventricles begin to contract shortly before ventricular systole and maintain tension throughout ventricular contraction. This prevents regurgitation (backward flow of ventricular blood into the atrial cavities) by bracing the atrioventricular valves against prolapse (being forced back into the atria by the high pressure in the ventricles).