Heart valves - view from above
There are four valves located in the heart. Each valve consists of either two or three folds of thin tissue. When closed, the valve prevents blood from flowing backwards to its previous location. When open the valve allows blood to flow freely. Valve problems can occur because of inborn (congenital) abnormalities, rheumatic fever, infection, or other causes.
Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Senior Physician, Massachusetts General Hospital.
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