Effusion: Too much fluid, an outpouring of fluid. For example, a pleural effusion is an abnormal accumulation of fluid in the pleural space between the lungs and the chest wall, while a knee effusion is an abnormal amount of fluid in the knee joint. A hemorrhagic effusion contains blood in the fluid.
Quick GuideHeart Disease: Causes of a Heart Attack
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Last Editorial Review: 3/19/2012