Definition of Effusion, pericardial

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Effusion, pericardial: Too much fluid within the fibrous sac (pericardium) that surrounds the heart. The inner surface of the pericardium is lined by a layer of flat cells (mesothelial cells) that normally secrete a small amount of fluid, which acts as a lubricant to allow normal heart movement within the chest. A pericardial effusion involves the presence of an excessive amount of pericardial fluid, a pale yellow serous fluid, within the pericardium.