Developmental considerations of mitral valve anomalies.

Atrioventricular valve development is described as following the general principle of junctional invagination and myocardial undermining. We have added considerations of the topographic relations of the developing mitral valve to these principles. Two groups of malformations are then distinguished: the first comprises disturbances of the general principle, the second is related to topographic abnormalities. It is shown that the atrioventricular septal defect, the straddling mitral valve and the isolated mitral cleft all have their own specific developmental backgrounds.