Aortic Valve

The aortic valve is one of the two semilunar valves of the heart, located between the left ventricle and the ascending aorta. It ensures unidirectional blood flow from the heart into the systemic circulation by preventing backflow of blood into the left ventricle during diastole. The valve operates passively, opening and closing based on pressure gradients between the left ventricle and aorta.

Location

The aortic valve is located at the outflow tract of the left ventricle, just below the origin of the ascending aorta. It lies posterior and to the right of the pulmonary valve. Anatomically, it is deep within the thorax, roughly behind the left side of the sternum at the level of the third intercostal space.

Structure

The aortic valve consists of three semilunar cusps that form pocket-like flaps. These are attached to the wall of the aortic root and work together to prevent regurgitation of blood during diastole.

Cusps

• Right cusp: Gives rise to the right coronary artery
• Left cusp: Gives rise to the left coronary artery
• Posterior (non-coronary) cusp: Does not give rise to a coronary artery

Each cusp has a central fibrous nodule and thinner lateral areas known as lunules. These structures ensure tight closure during diastole to prevent any blood from flowing backward.

Aortic Sinuses (Sinuses of Valsalva)

Immediately above each cusp is a dilation in the wall of the aorta called an aortic sinus. These sinuses help direct blood into the coronary arteries during diastole.

• Right aortic sinus: Opens into the right coronary artery
• Left aortic sinus: Opens into the left coronary artery
• Posterior aortic sinus: Has no coronary artery

Function

The aortic valve functions to:

• Open during systole as the left ventricle contracts and ejects blood into the ascending aorta
• Close during diastole when aortic pressure exceeds ventricular pressure, preventing regurgitation

The geometry of the cusps and the presence of the sinuses reduce turbulence and help maintain laminar flow into the aorta.

Microscopic Anatomy

Like other cardiac valves, the aortic valve is made of three layers:

• Fibrosa: Collagen-dense central core providing structural integrity
• Spongiosa: Loosely arranged connective tissue acting as a shock absorber
• Ventricularis: Elastic fibers facing the left ventricle for recoil and closure support

The valve is covered by endothelium and is avascular, depending on diffusion from surrounding blood for nourishment.

Topographic Relationships

• Anterior: Pulmonary trunk
• Posterior: Anterior leaflet of the mitral valve
• Right: Interventricular septum and right atrium (upper region)
• Left: Left atrium and upper part of the left ventricle

Surface Landmark

The aortic valve is best auscultated in the right second intercostal space at the parasternal line. Though anatomically deep and leftward, the valve’s sounds radiate here due to the direction of blood flow and proximity to the chest wall.

Summary

• Valve type: Semilunar
• Number of cusps: Three (right, left, posterior)
• Associated sinuses: Right and left give rise to coronary arteries
• Function: Prevents backflow into left ventricle
• Best heard: Right second intercostal space