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Damaged aortic valve. Coloured transoesophageal echo (TOE) ultrasound scan of blood flow through a damaged aortic valve (top left of purple area). The flow should be regular and smooth, but the different colours show turbulence in the flow. The damage may be caused by the build up of fatty plaques (atherosclerosis) or infection. Symptoms include breathlessness, angina (heart pain) and heart enlargement. There are four valves in the human heart, all of which prevent the backflow of blood. Damage to the valves can lead to malfunctioning of the heart and death. If a damaged valve cannot be repaired it must be replaced. (KEYSTONE/SCIENCE PHOTO LIBRARY/ANTONIA REEVE/SCIENCE PHOTO LIBRARY)