What term describes a malfunctioning valve that allows blood to flow backward?

A malfunctioning valve that allows blood to flow backward is referred to as an incompetent valve. This term specifically indicates that the valve does not close properly, resulting in regurgitation where blood flows in the reverse direction instead of forward through the heart or circulatory system. This condition can occur in various heart valves, leading to inefficient blood circulation and increased workload on the heart.

While conditions such as mitral regurgitation and tricuspid insufficiency describe specific types of valvular dysfunctions where backward flow occurs in the mitral and tricuspid valves, respectively, the term "incompetent valve" broadly encompasses any valve failing to function correctly, including these specific cases. Aortic stenosis, on the other hand, refers to a narrowing of the aortic valve, which impedes forward blood flow, rather than causing backward flow. Therefore, the most general and correct term to describe a valve that is allowing backward blood flow is indeed an incompetent valve.