Congenital bicuspid aortic valves are of two types, those consisting of two normal cusps and those in which one of the two cusps is subdivided by a ridge of congenital origin into two segments. The first type is evidently due to improper development of the endocardial swellings in the truncus arteriosus that form the rudimentary cusps or possibly to faulty growth of the aortic septum which normally bisects the two lateral endocardial cushions. In the second type there is maldevelopment of a commissure due to arrested growth of the annulus fibrosus and of the projections of the annulus that normally form the commissural cusp margins. The congenital ridge thus represents an abortive and deformed commissure.
A recent survey of records of 3,300 consecutive autopsies at the Institute of Pathology of the University Hospitals of Cleveland revealed 18 cases of congenital bicuspid aortic valve. Nine of these occurred among newborn and