The aortic valve is the main outlet valve for the heart. The left ventricle is the chief pumping chamber that pumps oxygenated blood through the aortic valve into the aorta, and then to all parts of the body. This valve has three thin cusps or leaflets (see side-on view in Figure 1), that open and close passively. This is a one-way valve, that when open, exhibits a valve area of 2 –4 square centimetres (cm²). Under normal circumstances, the valve should close completely and not allow any leakage of blood back in to the heart.

As can be seen from Figure 2, the pulmonary valve is an identical three cusp valve (both aortic and pulmonary valves seen from above in Figure 2), that normally, when open, allows de-oxygenated blood to be pumped from the right ventricle to the lungs (for oxygenation) via the pulmonary artery). Note its close proximity to the aortic valve, which enables it to be used to replace the aortic valve, in the Ross procedure.