Final answer:
Papillary muscles contract to generate tension on the chordae tendineae, preventing the atrioventricular valve flaps from being forced back into the atria and preventing backflow of blood during ventricular contraction.
Step-by-step explanation:
The papillary muscles function to prevent backflow of blood from the ventricles back into the atria. When the ventricles contract, blood is pushed toward areas of lower pressure, which would be back into the atria if not for the closure of the tricuspid and mitral (bicuspid) valves. The papillary muscles do this by contracting and generating tension on the chordae tendineae, which keeps the valve flaps from being forced into the atria and stops the backflow of blood, also known as regurgitation, during the contraction of the ventricles.