The aortic valve is one of the four valves which control the blood flow through the heart. It is located at the outlet of the left ventricle at the beginning of the ascending aorta (see yellow circle, Image 1). The healthy valve opens with minimal resistance and closes to prevent back flow into the ventricle.
The cardiac cycle can be divided into a systolic and diastolic interval, see Image 2. During systole an isochoric contraction of the left ventricle is followed by the ejection of blood into the aorta. During this interval the aortic valve remains open.
At diastole an isochoric relaxation precedes a filling of the left ventricle with blood from the atria. During this interval the aortic valve remains closed. Both mechanical and kinematic aspects are involved in valve functioning and differ in importance during the course of the cardiac cycle.
In one cardiac cycle three main phases can be distinguished in valve performance: (i) the opening and (ii) closing phases during systole and (iii) the closed phase during diastole. For a healthy valve, the opening interval is very fast (25 to 35 [ms]). The leaflets begin to bulge towards the aorta wall just before ventricular ejection begins. At the time when the flow in the ascending aorta has reached 75% of its maximum, the valve is completely open. In the case of normally working heart valves, the fluid flow remains laminar, although the Reynolds number reaches up to 4500 at peak flow [2]. Only when a valve exhibits a malfunctioning, some turbulence might be expected [1].

The natural valve consists of three highly flexible leaflets and three sinus cavities, see Image 3. Each leaflet can be divided in two functional areas:
The area near the free edge is known as the coaptive area (also called the lunulea because of its semilunar shape). When the valve is closed the outlet orifice of the left ventricle is sealed because the lunuleae of adjacent leaflets touch each other. In the middle of the free edge of each lunulea a structural thickening (’nodulus of Arantius’) is located. Presumably, it acts as a structural reinforcement, allowing a significant reduction in the height of the lunulea without causing central regurgitation during a closed valve configuration.
The remaining, non-coaptive area of the leaflet surface is referred to as the load bearing portion. This part constitutes a fiber-reinforced composite texture of elastin. The fibers consist mainly of collagen embedded in a matrix of endothelial cells. In particular, this texture has a three-layered structure: The ventricularis at the ventricular surface contains elastin and collagen fibers, the spongiosa (middle layer) contains acid mucopolysaccharides and some collagen fibers, the fibrosa (near the aortic surface) contains a dense network of collagen fibers. A similar layered structure is present in the lunulea, however, the arrangement of the fibers may be very irregular.

The deformation of both the leaflets and the ascending aortic wall as well as the velocity vector field is given in Image 4 (a) to (f). In frame (a) the valve is shown in its initial (stress free) configuration, corresponding to the closed position. During the acceleration phase (frame (b)) a forward flow is observed throughout the whole fluid domain, including the sinus cavity (i.e. wash-out). For the fully opened valve (frame (d)) the flow is concentrated in the center. Almost no flow can be seen in the sinus cavity. At the moment of complete valve opening, however, the flow has started to decelerate already. During the deceleration phase recirculation at the leaflet free edge precedes vortex development in the sinus cavity and the valve is closed again (frames (e) and (f)).