Aortic valve

The aortic valve is a semilunar valve located at the junction between the left ventricle and the ascending aorta. It ensures unidirectional blood flow from the left ventricle into the systemic circulation and prevents regurgitation during diastole.

The aortic valve is situated within the left ventricular outflow tract (LVOT), at the level of the cardiac skeleton. It lies dorsocranial to the left atrioventricular (mitral) valve and is centrally positioned within the cardiac base. Externally, it corresponds approximately to the left side of the cardiac base, near the third intercostal space.

The aortic valve is composed of three semilunar cusps (valvulae semilunares), forming a tricuspid structure. The cusps are:

• Right semilunar cusp (Right coronary cusp in humans)

• Left semilunar cusp (Left coronary cusp in humans)

• Septal semilunar cusp (Non-coronary cusp in humans)

Each cusp of aortic valve is thin, pocket-shaped, and attached along its convex border to the fibrous aortic annulus. The free edge of each cusp faces the lumen of the aorta and contains a central thickening called the nodule of semilunar cusps (nodulus valvulae semilunaris). On either side of the nodule is a thin crescentic portion known as the lunule of semilunar cusps.

Behind each cusp is a dilation of the aortic root called an aortic sinus (sinus of Valsalva in human anatomy). The right and left aortic sinuses give rise to the right and left coronary arteries, respectively. The non-coronary sinus does not give rise to a coronary vessel.

Each cusp consists of three histologic main layers:

• Fibrosa (aortic side): dense collagenous connective tissue providing tensile strength.

• Spongiosa (middle layer): loose connective tissue rich in proteoglycans, allowing flexibility and shock absorption.

• Ventricularis (ventricular side): rich in elastic fibers, facilitating rapid recoil during valve closure.

The cusps are covered on both sides by endothelium continuous with the endocardium of the ventricle and the intima of the aorta.

During ventricular systole, increased left ventricular pressure forces the cusps outward against the aortic wall, opening the valve and allowing blood ejection. During diastole, when ventricular pressure falls below aortic pressure, blood fills the aortic sinuses and pushes the cusps toward the center, causing coaptation of the lunulae and nodules and effective closure of the orifice.

The aortic annulus is part of the fibrous cardiac skeleton, providing structural support and maintaining the geometry of the valve orifice.