SOVEREIGN, ISM / SCIENCE PHOTO LIBRARY SOVEREIGN, ISM / SCIENCE PHOTO LIBRARY
Heart valve defect. Doppler ultrasound scan of a heart, showing blood flow (coloured area) through a failing mitral valve. The flow should be regular and smooth, but the different colours show turbulence in the flow. This scan passes vertically through the heart, with the heart's four chambers seen as the black areas. The central white areas are the walls and valves separating the chambers. The top two chambers are the atria, and the bottom two chambers are the ventricles. Depending on the cause, the valve may need to be replaced with an artificial one. Doppler ultrasound scanning uses high-frequency sound waves and the Doppler effect to measure the speed of moving fluids inside the body.
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