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Cardiac Valvular Apparatus

Q: Which heart valves belong to the atrioventricular group?

Two heart valves belong to the atrioventricular group. Tricuspid valve — located at the border of the right atrium and right ventricle, consisting of three cusps.Mitral valve (bicuspid valve) — located at the border of the left atrium and left ventricle, consisting of two cusps.

Q: How many cusps does a normal aortic valve have?

Normally, the aortic valve consists of three cusps. Left coronary cusp — one of the anatomical landmarks of the valve.Right coronary cusp — the second cusp in the structure.Non-coronary cusp — the third cusp of the aortic valve.

Apparatus valvularis cordis

For medical students2 min readUpdated 2026-10-10

The cardiac valvular apparatus is a complex of structures ensuring strictly unidirectional blood flow through the cardiac chambers and great vessels. Valve mechanics are inextricably linked to electrical processes within the myocardium, particularly the sequential resolution of excitation across different regions of the ventricles.

Mitral valveFunctions in two main states: fully open (O) and fully closed (C).

Aortic valveHas two cross-sectional configurations: leaflets coapted centrally or pressed against the walls.

Papillary musclesRecover from excitation last, preventing leaflet prolapse.

TP segmentReflects the period of complete electrical quiescence in the heart muscle.

Mechanics of the Valvular Apparatus

Graphical representation of valve function demonstrates a clear alternation of phases. To understand intracardiac hemodynamics, it is traditional to examine the key structures of the left heart:

IV. Mitral valve. Its cycle features two diametrically opposed positions. State "C" (Closed) means the valve is completely shut, isolating the left ventricular cavity from the left atrium. State "O" (Open) indicates that the valve is open, allowing ventricular filling.
V. Aortic valve. Similar to the mitral valve, its mechanics are described by alternating between state "C" (closed) and state "O" (open), which regulate blood ejection into the systemic circulation.

Functional Anatomy of the Aortic Valve

Analyzing the cross-section of the aortic root reveals strictly two states of the valve that determine hemodynamics in this region. No third or intermediate functional states exist in this context.

State "C" (Closed). In this phase, all aortic valve leaflets coapt tightly right at the center of the vessel. As a result, the aortic lumen is completely sealed, blocking retrograde blood flow back into the ventricle.
State "O" (Open). During blood ejection, the leaflets part and press maximally against the inner walls of the aorta. This ensures completely free, laminar blood flow directed into the great vessel (traditionally indicated on diagrams by a vector or arrow).

Physiology of Myocardial Repolarization

Proper function of the valvular apparatus, especially the atrioventricular valves, directly depends on electrical processes in the myocardium—specifically repolarization (the disappearance of excitation). This process does not occur simultaneously, but in a strict physiological sequence:

Excitation subsides first in the region of the interventricular septum.
Repolarization then encompasses the lateral walls of the ventricles.
Last of all, electrical activity disappears in the papillary muscles and trabeculae.

Complete cessation of electrical activity across all cardiac structures graphically corresponds to the TP segment. At this moment, the heart experiences complete electrical quiescence.

Role of Papillary Muscles and Trabeculae

The delayed repolarization in structures anchoring the valves is of immense physiological significance.

Because the papillary muscles and trabeculae recover from excitation last, their contraction lasts longer than that of the free ventricular walls. This prolonged, continuous tension is necessary to securely hold the leaflets of the atrioventricular (including mitral) valves at the very end of ventricular systole. This mechanism prevents the pathological inversion (opening) of the leaflets toward the atrial cavities under high intraventricular pressure.

Mnemonic

To remember the order of repolarization, use the rule "From Center to Anchors": septum first (center), then walls (periphery), and finally papillary muscles (valve anchors).

Frequently asked questions

Which heart valves belong to the atrioventricular group?

Two heart valves belong to the atrioventricular group.

Tricuspid valve — located at the border of the right atrium and right ventricle, consisting of three cusps.
Mitral valve (bicuspid valve) — located at the border of the left atrium and left ventricle, consisting of two cusps.

How many cusps does a normal aortic valve have?

Normally, the aortic valve consists of three cusps.

Left coronary cusp — one of the anatomical landmarks of the valve.
Right coronary cusp — the second cusp in the structure.
Non-coronary cusp — the third cusp of the aortic valve.

What mechanisms create the pressure gradient required to open the aortic valve?

The pressure gradient for opening the aortic valve is generated during the period of ventricular myocardial tension. Because all valves are closed and blood is incompressible, chamber volume remains constant. Synchronous isometric contraction of cardiomyocytes occurs (overall myocardial length does not decrease), leading to a sharp rise in intraventricular pressure. Once left ventricular pressure reaches the threshold value of approximately 80 mmHg, the semilunar aortic valve opens.

What phases and periods are distinguished in the structure of ventricular systole?

Ventricular systole comprises two sequential periods, each including two phases:

Period of tension — consists of the phase of asynchronous contraction and the phase of isometric contraction.
Period of ejection — consists of the rapid ejection phase and the reduced ejection phase.

How does intracardiac hemodynamics change in mitral valve prolapse?

Mitral valve prolapse involves the billowing of mitral leaflets into the left atrial cavity during left ventricular systole. This can lead to mitral regurgitation, causing a fraction of blood to flow backward from the left ventricle into the left atrium. Regurgitation is not an obligatory component, and its degree varies. When mitral regurgitation develops, it results in volume overload of the left atrium.

How does the aortic valve appear in the closed state on a cross-section?

Its leaflets coapt completely in the center of the aortic lumen, hermetically sealing off the blood flow.

Why is prolonged contraction of the papillary muscles necessary?

It prevents the atrioventricular valve leaflets from everting back into the atria under blood pressure at the end of ventricular systole.

What does the TP segment signify?

The TP segment is registered during the complete physiological absence of electrical excitation across all cardiac structures.

Go deeper

Hemodynamic parameters during phases "O" and "C" of the mitral valve
Detailed analysis of valvular apparatus function graphs
The relationship between the TP segment and mechanical diastole of the heart
The effect of pressure on pressing aortic valve leaflets against the vessel walls