Which heart valve condition involves non-functional or weakened mitral valves?

Mitral valve prolapse is characterized by the weakening or improper functioning of the mitral valve, which is located between the left atrium and left ventricle of the heart. In this condition, the valve's leaflets become enlarged or floppy and may bulge (prolapse) back into the left atrium during the heart's contraction. This can lead to symptoms such as palpitations, chest pain, or even shortness of breath in some individuals, although many remain asymptomatic.

On the other hand, the other conditions listed involve different aspects of heart valve function. Aortic stenosis primarily affects the aortic valve and involves narrowing that impedes blood flow from the heart. Tricuspid regurgitation involves the tricuspid valve, where blood flows backward into the right atrium. Pulmonary stenosis relates to the narrowing of the pulmonary valve, affecting blood flow to the lungs. None of these conditions specifically describe issues with the mitral valve itself, making mitral valve prolapse the correct choice for a condition that involves non-functional or weakened mitral valves.