Overview

Number of cusps2 (anterior, posterior)

Normal orifice area4–6 cm²

Severe stenosis≤1.5 cm²

Auscultation areaApex: 5th left intercostal space, midclavicular line

Annulus and leaflets. The mitral annulus is saddle-shaped, or D-shaped in plan. The anterior leaflet is large and is fibrously continuous with the aortic valve (the aortomitral curtain), so it forms part of the wall between inflow and outflow tracts. The posterior leaflet runs further around the annulus but is shallower. It is usually divided into three scallops, P1–P3 in Carpentier's nomenclature, which face the A1–A3 segments of the anterior leaflet. The leaflets meet at the anterolateral and posteromedial commissures, and chordae from both papillary muscles insert into both leaflets.

The mitral apparatus. A competent valve depends on all of its parts: annulus, leaflets, chordae, papillary muscles and left ventricular wall. Disease of any one of them can cause regurgitation.

Size and sound. The normal orifice area is 4–6 cm². Mitral closure (M1) is the first and loudest component of S1.

Location: Behind the left half of the sternum at the level of the 4th costal cartilage. It is best heard at the apex (left 5th intercostal space, midclavicular line).

Parts & subdivisions

Anterior (aortic) leaflet
Large and semicircular, continuous with the aortic valve. Its segments are labelled A1–A3.
Posterior (mural) leaflet
Crescentic, with three scallops (P1–P3). It is the leaflet most often involved in prolapse.
Commissures
Anterolateral and posteromedial.
Subvalvular apparatus
The chordae tendineae and the two papillary muscles.

Function

Allows blood to flow from the left atrium into the left ventricle during diastole.
Prevents blood flowing back into the left atrium and pulmonary veins during systole.

Clinical significance

Mitral stenosis

Mitral stenosis is almost always rheumatic. The commissures fuse and the chordae thicken, producing a "fish-mouth" orifice. Pressure backs up behind it, causing left atrial dilatation, atrial fibrillation, pulmonary venous hypertension and eventually right heart failure.

Signs are a loud S1, an opening snap and a low-pitched mid-diastolic rumble at the apex, best heard with the bell of the stethoscope with the patient on their left side. There may be a malar flush. Stenosis is severe when the valve area is ≤1.5 cm². Treatment is percutaneous balloon commissurotomy or valve replacement.

Mitral regurgitation

Causes include degenerative disease (prolapse, flail leaflet), functional regurgitation from left ventricular dilatation or ischaemia, endocarditis, rheumatic disease and papillary muscle rupture. It produces a pansystolic murmur at the apex radiating to the axilla. Acute severe regurgitation causes sudden ("flash") pulmonary oedema. Treatment options are surgical repair (preferred), replacement or a transcatheter edge-to-edge repair device.

Mitral valve prolapse

In mitral valve prolapse, myxomatous leaflets thicken and billow back into the left atrium. It affects about 2–3% of people. It produces a mid-systolic click, sometimes with a late systolic murmur, and is associated with Marfan and Ehlers–Danlos syndromes.

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.