Final answer:
The mitral valve would be affected by the failure of the papillary muscles and/or chordae tendineae since these structures are not associated with the semilunar valves (aortic and pulmonary) but are crucial for the function of the atrioventricular valves (tricuspid and mitral).
Step-by-step explanation:
If the papillary muscles and/or chordae tendineae stopped functioning, the valve that would be affected would be the mitral valve. The papillary muscles and chordae tendineae are structures associated with the atrioventricular valves (tricuspid and mitral) of the heart. They are critical for preventing the backflow of blood into the atria when the ventricles contract. On the other hand, the aortic and pulmonary valves do not have these structures since they are semilunar valves and function differently. These semilunar valves do not require papillary muscles or chordae tendineae because they close due to changes in blood pressure that occur during the cardiac cycle. Therefore, these valves are not affected if the papillary muscles and chordae tendineae were to fail.