A prosthetic caged-ball aortic valve that can be placed with transcatheter techniques was designed, constructed, and initially evaluated in 12 adult mongrel dogs. The prosthesis consisted of a ring, cage, and ball. The ring was made of stainless steel wire coiled in a springlike configuration and covered with an expandable nylon mesh. The cage consisted of a self-expanding Gianturco stent with flat stainless steel wires attached across the cranial end. The ball was a detachable latex balloon filled with a radiopaque silicone prepolymer system. The self-expanding valve was easily passed through an 11- or 12-F Teflon sheath and was placed in the ascending aorta by means of the carotid approach. The stability and efficacy of the prosthesis were evaluated radiographically for as long as the valve remained functional (1-3 hours). The competency of the valve and the patency of the coronary arteries were determined angiographically over the same period. The results of these studies indicate that development and transcatheter placement of a prosthetic aortic valve are feasible.