What is endocarial cushion defect?

AV valve development: In normal development, the primitive atrioventricular (av) canal joins the atria to the ventricles. At four to five weeks of gestation, the superior and inferior endocardial cushions of the common av canal fuse and lead to the formation of the mitral and tricuspid valves and the av septum. Failure of these cushions to fuse properly results in a broad range of av septal defects and av valve defects.