An artificial heart valve is a device which is implanted in the heart of patients who suffer from valvular diseases in their heart. When one or two of the four heart valves of the heart have a malfunction, the choice is normally to replace the natural valve with an artificial valve. This requires open-heart surgery. Valves are integral to the normal physiological functioning of the human heart. Natural heart valves...
I am a deer hunter as well, the deer will more than likely sense your worrying over the thoughts you are having with your dads valve, just relax out there!!...
Here are lots of pictures:
http://images.google.com/images?sourceid=navclient&ie=UTF-8&rlz=1T4GGLJ_enUS211US211&q=artificial heart valve
It's probably plastic.