Cardiac Valves & Subvalvular Apparatus

Aortic Valve

The aortic valve (AV) is a trileaflet semilunar valve separating the LV outflow tract from the aortic root. Its three cusps — right coronary cusp, left coronary cusp, and non-coronary cusp — are named for whether a coronary artery ostium originates from the corresponding aortic sinus (sinus of Valsalva) directly above that cusp. The right coronary artery arises from the right sinus and the left main coronary artery arises from the left sinus; no coronary ostium sits above the non-coronary cusp. Unlike the atrioventricular (AV) valves, the aortic valve has no chordae tendineae or papillary muscles — it is a passive, pressure-driven flap valve that opens in systole and closes by leaflet coaptation in diastole. There is no discrete fibrous "ring" analogous to the mitral annulus; instead the functional aortic annulus is the virtual ring at the basal attachment of the three cusps, part of the fibrous skeleton of the heart.

Pulmonic Valve

The pulmonic valve is also a trileaflet semilunar valve, structurally similar to the aortic valve, separating the RV outflow tract (infundibulum) from the main pulmonary artery. Its three cusps are conventionally described as anterior, right, and left. It is the most anterior and most superior of the four cardiac valves and, like the aortic valve, has no chordae or papillary muscles.

Mitral Valve

The mitral valve (MV) is the left-sided atrioventricular valve, and unlike the semilunar valves it is bileaflet: an anterior (aortic) leaflet and a posterior (mural) leaflet. The anterior leaflet is larger, semicircular, and shares fibrous continuity with the aortic root (the aortomitral curtain); the posterior leaflet is shorter but has a longer attachment along the annulus and is divided into three scallops — P1 (lateral), P2 (middle), P3 (medial) — with corresponding, though less distinct, anterior segments A1, A2, and A3 (Carpentier nomenclature), used throughout the exam blueprint to localize prolapse and flail segments.

The mitral annulus is a saddle-shaped, D-shaped fibrous structure — part of the fibrous skeleton anteriorly (continuous with the aortic annulus) but less fibrous and more muscular posteriorly, which is why annular dilation and calcification predominate posteriorly.

Tricuspid Valve

The tricuspid valve (TV) is the right-sided atrioventricular valve and has three leaflets: anterior (largest), posterior, and septal. The septal leaflet attaches directly to the interventricular septum near the membranous septum and AV node — a key surgical and electrophysiologic landmark. The tricuspid valve is normally the most apically displaced of the four valves; on the apical 4-chamber view the septal tricuspid leaflet inserts slightly closer to the apex than the anterior mitral leaflet (normal offset is small — marked apical displacement defines Ebstein anomaly, covered in the congenital chapter). The tricuspid annulus is larger and less fibrous than the mitral annulus, making it more prone to functional dilation and secondary regurgitation.

The Subvalvular Apparatus

Both atrioventricular valves — but not the semilunar valves — depend on a subvalvular apparatus of chordae tendineae and papillary muscles to prevent leaflet prolapse into the atrium during systole:

• Chordae tendineae are thin fibrous cords connecting the leaflet undersurface to the papillary muscle tips. They are classified by insertion site: primary (marginal) chordae attach at the free leaflet edge and are the main barrier to prolapse; secondary (strut) chordae attach to the leaflet body and support annular geometry and LV systolic function; tertiary (basal) chordae, present mainly on the posterior mitral leaflet, run directly from papillary muscle or ventricular wall to the leaflet base.
• Mitral papillary muscles: an anterolateral papillary muscle, usually supplied by a single arterial source (branches of the LAD and/or LCx — "dual" supply in most hearts), and a posteromedial papillary muscle, usually supplied by a single dominant vessel (typically the posterior descending artery, most often from the RCA in a right-dominant circulation). Because it more often relies on a single coronary source, the posteromedial papillary muscle is more vulnerable to ischemic rupture than the anterolateral muscle — a frequently tested point connecting anatomy to acute MI complications.
• Tricuspid papillary muscles: an anterior papillary muscle (largest, associated with the moderator band), a posterior papillary muscle, and a septal papillary muscle (smallest, often small or absent, with some septal-leaflet chordae attaching directly to the septum without an intervening papillary muscle).

Comparing the Four Valves

Functional Integration

Normal valve competence requires every level of this apparatus to function together — annulus, leaflets, chordae, and papillary muscles. Dysfunction at any single level can produce regurgitation even when the leaflets themselves are structurally normal, which is why the Carpentier functional classification (Type I: normal leaflet motion with an annular or perforation problem; Type II: excess leaflet motion, e.g., prolapse or flail; Type IIIa: restricted leaflet motion in diastole, e.g., rheumatic disease; Type IIIb: restricted leaflet motion in systole, e.g., ischemic tethering) is applied primarily to mitral regurgitation and is explored further in the valvular pathology chapters.