Effusion, pericardial

Effusion, pericardial: Too much fluid within the fibrous sac (the 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 serous fluid of a pale yellow color, within the pericardium. The term "effusion" comes from the Latin "effusio" meaning a pouring out. A pericardial effusion is, literally, a pouring out of fluid around the heart.