Final answer:
The AV valves are supported by strong collagen cords called chordae tendineae ("heart strings"), which are anchored on papillary muscles protruding from the ventricular walls.
Step-by-step explanation:
The chordae tendineae are attached to papillary muscles that protrude from the ventricular walls, preventing the AV valves from inverting and causing backflow during ventricular contraction.
There are three papillary muscles in the right ventricle: the anterior, posterior, and septal muscles, which correspond to the three flaps of the tricuspid valve. These muscles contract during ventricular contraction, creating tension on the chordae tendineae to prevent the backflow of blood into the atria.