The Most Common Heart Valves Affected by Infective Endocarditis

Infective endocarditis primarily affects the heart's inner lining and is characterized by the formation of vegetations—clumps of bacteria, fibrin, and other inflammatory materials—on the heart valves. Among all heart valves, the mitral and aortic valves are most commonly involved.

Why the Mitral and Aortic Valves Are Frequently Affected

One of the main reasons these two valves are more susceptible is due to the natural blood flow dynamics within the heart. Microorganisms circulating in the bloodstream often travel from a high-pressure chamber to a low-pressure chamber through the valve openings. In patients with pre-existing valve conditions, such as mitral or aortic regurgitation, this blood flow becomes abnormal.

Role of Blood Flow in Infection Development

When regurgitation occurs, the affected area downstream experiences reduced blood flow, creating a low-shear environment. This environment is particularly favorable for microbial colonization and vegetation formation. As a result, bacteria tend to settle and multiply on these valves, leading to infection and tissue damage.

This localized stasis of blood flow not only promotes microbial adhesion but also limits the immune system's ability to clear the infection effectively. Therefore, the combination of altered hemodynamics and impaired immune response makes the mitral and aortic valves the most common sites for infective endocarditis to develop.