STEVE ALLEN / SCIENCE PHOTO LIBRARY STEVE ALLEN / SCIENCE PHOTO LIBRARY
Heart valve surgery. Artificial (prosthetic) heart valve being stitched, ready to be pulled into position in the heart during heart valve replacement surgery. Heart valves prevent blood from flowing back into the heart chamber after the blood is pumped out by the heart. Valve failure may be life-threatening. This is open heart surgery, where the chest cavity is opened up to access the heart during surgery.
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