Embryology of the mitral valve.

Development of the aortic (anterior) leaflet of the mitral valve was studied in human embryos from 3.6 to 25 mm crown-rump length. The notion that endocardial cushion tissue does not materially contribute to the atrioventricular valves has yet to be investigated for this particular leaflet. The study showed that the fused endocardial cushions act as an intermediary between the antero-superior and postero-inferior components of the valve leaflet. These latter components derive from the primary fold and the inlet septum, respectively. The cushion tissue itself is incorporated in a small portion of the leaflet which is continuous with the aortic-mitral intervalvar fibrous tissue.