Artificial mitral and aortic valves used to replace natural valves that have failed due to mitral stenosis. The valves are shown attached to tubes to demonstrate the way that they operate. Mitral stenosis occurs when the three flaps of the mitral valve in the left side of the heart begin to fuse together and prevent the normal flow of blood. It was a frequent long-term consequence of rheumatic fever, once a common childhood illnes, but could be treated by replacing the heart valves. The first human implant of an artificial valve was performed in 1952.
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