[Mesoscopic study of the mitral valve and its fibrous ring]

To study the spatial arrangement of the fibrous elements that form the leaflets of the mitral valve and its fibrous ring.

The study of 20 human adult hearts, of both sexes, fixed in 10% formaldehyde solution was made. The mitral valves with their fibrous rings and small parts of the adjacent atrial and ventricular muscles were removed. Part of this material was embedded in paraffin and cut serially at a thickness of 40 microns and stained by Azan's trichrome and by resorcin-fuccin and another was dissected under stereoscope in order to verify the arrangement of the myocardial bundles at the level of the fibrous ring.

It was observed that the fibrous ring is consisted of collagenous fibers which involved in an incomplete form the atrioventricular ostium, as they were absent in the anteromedial region of the ostium. The leaflets were made of collagenous fibers disposed parallel to the long axis of the valve. This collagenous fibers were covered by atrial and ventricular endocardium. The collagenous fibers of the leaflets were continuous, by their base, into the fibrous ring. It was observed, in a few cases, the presence of atrial muscle fibers into the anterior leaflet of the mitral, mainly in its central area.

The leaflets of the mitral valve and its fibrous ring have a structural continuity suggesting that elements would act synchronously in the closure of the atrioventricular ostium during ventricular systole. The contraction of the myocardial bundles fixed in the fibrous ring contributes to decrease the diameter of the mitral ring.