I've seen dynamic memory work better with other guests though, so it might be either something I'm doing wrong, or a side effect of the File Server role. Either way, I've gotten better results with setting static amounts of RAM on my file/DFS servers.
A biological heart valve is a heart valve recovered from a donor or created from donor tissue. A cadaveric valve comes from a human donor. Bovine valves are recovered from cows and porcine valves come from pigs.
Heart valves function to ensure a one-way flow of blood through the heart. The valves are not made of muscle, but rather are composed of sheets of tough connective tissue (leaflets) that act like flaps. The heart valves open and close passively because of pressure differences on either side of the valve.