Digital scan of a 35mm slide. Black-and-white comparison of three models of Starr-Edwards heart valves labeled (left-right: A 1200, B 2300, and C 2310. Each is a ball-and-cage style heart valve, Model 1200 has a plastic ball and models 2300 and 2310 have metal balls. Models 2300 and 2310 have a cage completely covered in white mesh cloth, while model 1200 has a cloth-covered ring only.