A new artificial aortic valve prosthesis was developed for implantation by the transluminal catheter technique without thoracotomy or extracorporal circulation. The new heart valve was prepared by mounting a porcine aortic valve into an expandable stent. Before implantation, the stent-valve was mounted on a balloon catheter and compressed around the deflated balloon. The stent-valve mounted balloon catheter was then advanced retrogradely to the ascending aorta or the aortic root in anaesthetized pigs. Implantation was performed by balloon inflation which expanded the stent-valve to a diameter exceeding the internal diameter of the vessel--thus ensuring a stable fixation against the vessel wall. A total of nine implantations were performed in seven 70 kg closed chest pigs. Sub- and supracoronary implantation was performed in two and three pigs, respectively, while implantation in both positions was done in two. Angiographic and haemodynamic evaluation after implantation revealed no significant stenosis (less than or equal to 16 mmHg) in any of the nine valves and trivial regurgitation in only two. Complications were associated with restriction of the coronary blood flow in three animals. This preliminary study indicates that artificial aortic valves can be implanted in closed chest animals by transluminal catheter technique.