Ultrastructure of the human aortic valve.

The human aortic valve is examined histologically by light, transmission electron and scanning electron microscopy. The observations show that the valve leaflets are multi-laminated structures, whose laminae do not have very distinct boundaries. Through the whole thickness of the leaflets, the load-bearing collagenous fibers are preferentially oriented in the transverse direction. Elastin networks are found only in the ventricular area. The leaflets attach themselves to the ventricular musculature through very dense collagenous meshworks known as the aortic ring. The whole structure is very efficient for its function of sustaining large pressures when closed and opening under minimal pressure gradients in systole.