MARTIN DOHRN / SCIENCE PHOTO LIBRARY. MARTIN DOHRN / SCIENCE PHOTO LIBRARY.
Surgery in progress to replace a damaged mitral heart valve: the heart is visible through the large incision made into the patient's chest wall. The mitral valve divides the left atrium and ventricle of the heart, and consists of two cusps (flaps). It allows blood to pass from atrium to ventricle, but prevents backflow. Damaged valves do not close properly and a reflux (backflow) of blood occurs, with potentially fatal results. Many types of artificial valves exist, some made from metal and fabrics. In this operation the replacement valve was made from natural tissue, obtained from porcine pericardium (the tough membrane that surrounds a pig's heart).
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