This free floating artificial heart valve was the second type of prosthetic designed by pioneering heart surgeon Dr. Charles Hufnagel (1916-1989) and his team at Georgetown University. It was made of polypropylene. The disk initially received a coating of silicone rubber to ensure it did not make a loud noise. The valve could be implanted in the aortic and mitral and tricuspid valves. First clinically used in 1963, many of these early valves were still in use ten years later.