ANTONIA REEVE / SCIENCE PHOTO LIBRARY ANTONIA REEVE / SCIENCE PHOTO LIBRARY
Prosthetic heart valves. Boxes of different sized prosthetic (artificial) heart valves. There are four valves in the human heart, all of which prevent the backflow of blood. Damage to the valves can lead to malfunctioning of the heart and death. If a valve cannot be repaired it must be replaced.
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