Fig. 2.

The microarchitecture of adult cardiac valves. (A,B) The stratified structure of aortic (A) and mitral (B) cardiac valves ensures unidirectional blood flow. Valve leaflets are composed of three layers of stratified extracellular matrix, including an elastin-rich ventricularis layer in the SL valves or the atrialis layer in the AV valves (purple), a proteoglycan-rich spongiosa layer (light blue) and a collagen-rich fibrosa layer (yellow), interspersed with valve interstitial cells (VICs) and sheathed in a monolayer of valve endothelial cells (VECs). The direction of pulsatile blood flow in relation to valve leaflets is indicated (red arrows). The microarchitecture of an aortic valve leaflet ensures blood moves from the ventricle to the aorta. The microarchitecture of a mitral valve leaflet is supported by the chordae tendineae, which ensure blood flow from the atrium to the ventricle. AV, atrioventricular; SL, semilunar.