Which heart valve is most commonly affected in rheumatic heart disease?

Rheumatic heart disease primarily affects the mitral valve due to the autoimmune response following an infection with Group A Streptococcus, which causes rheumatic fever. The inflammatory process leads to chronic scarring and deformity of the mitral valve, resulting in complications such as mitral stenosis and mitral regurgitation. The mitral valve is the most frequently involved valve because it experiences the most hemodynamic stress in the heart, particularly during left ventricular contraction. Consequently, it is more susceptible to the pathological changes associated with rheumatic fever.

In contrast, while other valves can be affected in rheumatic heart disease, they are significantly less common. The aortic valve does experience some involvement but not as frequently as the mitral valve. The tricuspid and pulmonic valves are rarely affected in the context of rheumatic heart disease, making them less relevant in this discussion. Therefore, the mitral valve's central role in the pathology of rheumatic heart disease underscores why it is considered the valve most commonly affected.