Atrioventricular or Cuspid Valves
These are small valves that prevent backflow from the ventricles into the atrium during systole. They are anchored to the wall of the ventricle by chordae tendineae, which prevent the valve from inverting.
The chordae tendineae are attached to papillary muscles that cause tension to better hold the valve. Together, the papillary muscles and the chordae tendineae are known as the subvalvular apparatus. The function of the subvalvular apparatus is to keep the valves from prolapsing into the atria when they close. The subvalvular apparatus have no effect on the opening and closure of the valves, however. This is caused entirely by the pressure gradient across the valve. The peculiar insertion of chords on the leaflet free margin however provides systolic stress sharing between chords according to their different thickness.
The closure of the AV valves is heard as the first heart sound (S1).
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