ANTONIA REEVE / SCIENCE PHOTO LIBRARY ANTONIA REEVE / SCIENCE PHOTO LIBRARY
Artificial heart valve before surgical implantation. The four heart valves prevent blood from re-entering each of the heart chambers once it has left. If one of these valves becomes narrowed or leaky, due to damage or disease for example, it must be replaced with a prosthetic valve.
Model release not required. Property release not required.