We developed a new valved conduit with commissures using a glutaraldehyde preserved equine pericardium, and implanted this prosthesis between the right ventricle and the pulmonary artery in the dog to examined the movement of the valve. Our new prosthesis consists of a conduit and three leaflets. Each leaflet is sutured to the inner surface of the conduit to form a valve. The adjacent free edges of the leaflets are sutured together by placing a mattress stitch 2 mm from their attachment to the conduit so that the leaflets form commissures. These commissures are designed to facilitate prompt coaptation of the three leaflets in diastole. A radiopaque marker is anchored to the center of the free edge of each leaflet and to the outer surface of the conduit to investigate its movement. The movement of the radiopaque markers studied by cineangiography revealed good coaptation of three leaflets in diastole and their full opening in systole. These findings demonstrated that the valve in our prosthesis might function well to prevent regurgitation across it.