The mitral annulus is a fibrous ring that is attached to the mitral valve leaflets. Unlike prosthetic valves, it is neither circular nor continuous. The annulus contracts and reduces its surface area during systole to help provide complete closure of the leaflets. Annular dilatation can result in poor leaflet apposition, leading to mitral regurgitation

Mitral regurgitation

Mitral regurgitation , mitral insufficiency or mitral incompetence is a disorder of the heart in which the mitral valve does not close properly when the heart pumps out blood. It is the abnormal leaking of blood from the left ventricle, through the mitral valve, and into the left atrium, when...

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The normal diameter of the mitral annulus is 3.1 ± 0.4 cm, and the circumference is 8 to 9 cm. There is no histologic evidence of an annular structure anteriorly, where the mitral valve leaflet is contiguous with the posterior aortic root.