The human heart is a four-chambered muscular pump divided into right and left sides, each containing an atrium (upper, receiving chamber) and a ventricle (lower, pumping chamber). The right heart receives deoxygenated blood from the body (via superior and inferior vena cava into the right atrium) and pumps it to the lungs via the pulmonary artery for oxygenation (pulmonary circuit). The left heart receives oxygenated blood from the lungs (via pulmonary veins into the left atrium) and pumps it to the body via the aorta (systemic circuit). The left and right sides are separated by the interventricular septum (between ventricles) and interatrial septum (between atria). The left ventricle has a much thicker muscular wall than the right ventricle, reflecting its greater workload in pumping blood through the high-resistance systemic circulation versus the low-resistance pulmonary circulation.

The atrioventricular (AV) valves separate the atria from the ventricles and ensure unidirectional blood flow from atria to ventricles during diastole while preventing backflow during systole. Tricuspid valve (right AV valve): located between the right atrium and right ventricle; consists of three leaflets (cusps) — anterior (largest), posterior, and septal; each cusp is attached at its base to the fibrous AV ring (annulus fibrosus) and at its free edge to chordae tendineae — strong fibrous cords connecting the valve cusps to papillary muscles (specialised conical projections of ventricular myocardium). When the right ventricle contracts, the papillary muscles also contract, maintaining tension on the chordae tendineae and preventing the valve cusps from inverting into the atrium (preventing valve prolapse and regurgitation). Bicuspid/Mitral valve (left AV valve): located between the left atrium and left ventricle; consists of two leaflets — anterior (aortic) and posterior (mural); similarly attached to left ventricular papillary muscles via chordae tendineae; subjected to much higher pressures than the tricuspid valve due to the left ventricle's greater pressure generation, which explains why mitral valve disease is more common and clinically significant than tricuspid valve disease.

Semilunar valves (named for their half-moon shaped leaflets) guard the exits of both ventricles, preventing backflow of blood from the great arteries into the ventricles during diastole. Pulmonary valve: located at the junction of the right ventricle and pulmonary trunk; consists of three semilunar leaflets (anterior, left posterior, right posterior); opens when right ventricular pressure exceeds pulmonary artery diastolic pressure during systole, allowing blood ejection into the pulmonary circulation; closes when right ventricular pressure falls below pulmonary artery pressure at the end of systole, preventing backflow. Aortic valve: located at the junction of the left ventricle and aorta; consists of three semilunar leaflets (right coronary, left coronary, and non-coronary cusps — named for their relationship to the coronary artery ostia located in the aortic sinuses immediately above the valve leaflets); opens during left ventricular systole when LV pressure exceeds aortic diastolic pressure; closes during diastole when aortic pressure exceeds LV pressure, maintaining aortic diastolic pressure and coronary perfusion. Unlike AV valves, semilunar valves have no chordae tendineae or papillary muscles — their closure depends entirely on pressure differences and their structural geometry.

The familiar "lub-dub" heart sounds heard through a stethoscope are generated primarily by the closure of the cardiac valves. First heart sound (S1 — "lub"): caused by closure of both AV valves (tricuspid and mitral/bicuspid) at the beginning of ventricular systole. The mitral component (M1) is slightly earlier than the tricuspid component (T1). S1 is best heard at the apex of the heart. Second heart sound (S2 — "dub"): caused by closure of both semilunar valves (aortic and pulmonary) at the end of ventricular systole/beginning of diastole. The aortic component (A2) is slightly earlier than the pulmonary component (P2). S2 is best heard at the base of the heart (upper left sternal border for pulmonary, upper right sternal border for aortic). Abnormal heart sounds (murmurs) are generated by turbulent blood flow, typically caused by stenotic (narrowed) valves (causing systolic murmurs when AV valves are affected, diastolic murmurs when semilunar valves are affected) or regurgitant (leaking) valves (causing diastolic murmurs when AV valves leak, systolic murmurs when semilunar valves leak).