Heart Valves: Four Valves in Two Pairs—Structure, Function, and Clinical Relevance

The heart has four valves arranged in two pairs, ensuring unidirectional blood flow through the cardiac chambers.

Right Heart (Low-Pressure, Pulmonary Circuit)

• Tricuspid Valve: 3 leaflets; between right atrium and right ventricle. Prevents backflow into RA during ventricular systole.
• Pulmonary Valve: 3 semilunar cusps; between right ventricle and pulmonary artery. Prevents backflow into RV during diastole.

Left Heart (High-Pressure, Systemic Circuit)

• Mitral (Bicuspid) Valve: 2 leaflets (anterior, posterior); between left atrium and left ventricle. Supported by chordae tendineae and papillary muscles. Prevents backflow into LA.
• Aortic Valve: 3 semilunar cusps; between left ventricle and aorta. Prevents backflow into LV.

Valve Dynamics

• AV valves (tricuspid, mitral) open during diastole (ventricular filling); close at systole onset (S1 heart sound).
• Semilunar valves (pulmonary, aortic) open during systole (ejection); close at diastole onset (S2 heart sound).
• All valves are passive—no muscular tissue; they respond to pressure gradients.

Common Pathologies

• Stenosis: Narrowed orifice → pressure overload (AS, MS).
• Regurgitation: Incomplete closure → volume overload (AR, MR, TR, PR).
• Endocarditis: Vegetations on leaflets (esp. mitral, aortic).
• Prolapse: Myxomatous degeneration → floppy leaflets (MVP most common).

Echocardiography (transthoracic/transesophageal) is the primary imaging modality for valve assessment.