Definition While the term "aortic stenosis" appropriately might be applied to any one of several states in which the aorta or its first portion is congenitally hypoplastic or generally narrowed as the result of acquired disease, it usually is employed to designate a significant constriction of the orifice of the aortic valve itself. Congenital obstruction or narrowing of the left ventricular outflow tract, whether caused by a membrane, by a muscular shelf, or by simple hypoplasia, is referred to as subaortic stenosis, although in these same cases the valve itself also may be maldeveloped or hypoplastic. Anatomical aortic valvular stenosis usually implies stiffening of the leaflets or mutual cross adherence of their free margins with consequent reduction in the size of the valve aperture due to commissural obliteration. Since aortic stenosis is one of the most common of the various valvular deformities produced by rheumatic fever, being second in frequency