Left Ventricle (II)

This is a parasagittal section of the heart slightly to the left of the posterior aortic cusp.
The right side of the right half of the specimen is shownhere. The left side is shown in the image below. The left atrium appears as a smooth-walled chamber with a thicker, white endocardium. The left ventricle is divided anatomically into inflow, apical and outflow portions. The angle between the inflow and the outflow tracts is more acute than that found in the right ventricle. The inflow tract is funnel-shaped and surrounded by the mitral valve annulus, leaflets and chordae tendineae. The apical portion, including the apical two-thirds of the interventricular septum, has fine trabeculations. The apex is normally the thinnest portion of the left ventricle. The outflow tract is formed by the smooth basal (muscular) portion of the interventricular septum, the anterior ventricular wall and the anterior mitral leaflet. The muscular septum bulges into the left ventricular outflow tract. This sigmoid shape of the muscular septum becomes prominent with increasing age. The interventricular septum also has a membranous portion below the right and posterior (noncoronary) aortic cusps (arrowheads). This area is variable in size. Generally it is divided into an atrioventricular portion, between the right atrium and left ventricle, and an interventricular portion, by the insertion of the septal leaflet of the tricuspid valve.

In contrast to the right ventricle, where the tricuspid and pulmonic valves are separated by a muscular band, the left ventricle is characterized by fibrous continuity between the mitral and the aortic valves. The anterior mitral leaflet, being continuous with the left and posterior (noncoronary) aortic cusps (mitro-aortic continuity). This leaflet , divides the left ventricle into inflow and outflow portions. The mitral valve leaflets are anchored by the anterolateral and posteromedial papillary muscles. The aortic root clearly shows the sinotubular junction, a ridge formed at the border between the sinuses and the tubular segments of the ascending aorta. Tiny openings of Thebesian veins are seen, particularly in the posterior wall.  The arrowheads in the aorta point a the crease that divides the root from the aorta from the ascending aorta. This is the sinotubular junction.

The structure of the mitral valve is shown here.   The microscopic structure of the cardiac myocytes is discussed in the cardiac histology section, and the structure of the myofilaments in the molecular anatomy section.

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