Hypoplasia of the aortic valve annulus and ascending aorta is a rare form of congenital aortic stenosis, with a poor prognosis. Replacement of the aortic valve and ascending aorta with a suitable prosthesis is feasible, but the hypoplastic valve annulus must also be enlarged if an adult-sized aortic valve is to be placed in the subcornary position. In an effort to develop a new method of surgical treatment for this congenital abnormality, we fabricated a prosthesis which can be interposed between the left ventricular apex and descending thoracic aorta. This prosthesis is coupled to a 25 mm. Dacron graft and xenograft valve and is lined with flocked Dacron fibrils to encourage formation of a stable biologic lining and prevent thrombus buildup. The prosthesis was implanted in a 22 year old male patient of the Children's Hospital Medical Center without difficulty. Postoperative cardiac catheterization idicated that all of the contrast material was ejected from the left ventricle through the prosthesis. The patient was discharged from the hospital taking sodium warfarin and remains entirely asymptomatic.