Experiences with the repair of the mitral valve in mitral in competence.

The mitral valve comprises four structures: annulus fibrosus, cusp tissue, chordae tendineae, and papillary muscles. The annulus fibrosus is strong at the base of the aortic cusp, where it forms part of the aortic valve ring, and weak at the base of the mural cusp. From every part of the annulus cusp tissue hangs vertically downwards into the cavity of the left ventricle in the form of a short sleeve (Fig. 1). Medially and laterally the tissue is elongated, and thickened by the insertion of chordae tendineae, to form the major aortic and mural leaflets. Anteriorly and posteriorly cusp tissue exists in the form of a delicate junctional band that may contain minor leaflets (Chieche, Lees, and Thompson, 1956). In health there are no commissures (Fig. 2). In mitral stenosis division of the junctional band may cause severe regurgitation. Chordae tendineae arise from papillary muscles and fan out as they insert into the edges and ventricular surfaces of the major cusps. It is important to realize that each papillary muscle distributes chordae to both cusps in such a way that contraction of the muscle tends to approximate the cusps (Fig. 3). When the valve is closed the atrial surfaces of the major cusps have a wide area of contact, and eversion is prevented by chordae and papillary muscles. PATHOLOGICAL CHANGES