الفهرس 
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Abstract
Pericardium is a fibroserous sac that surrounds the heart and the roots of great vessels arising from or entering it, it is situated in the middle mediastinum, it consists of two sacs; the outer fibrous sac called ” Fibrous Pericardium” and the inner double-layered sac called ” Serous Pericardium. The serous pericardium is a closed serous sac that is invaginated from behind and above by the heart and the roots of its big vessels converting it to potential space called ”Pericardial Cavity” having two layers; visceral and parietal.
Under normal conditions, the human pericardial cavity contains 20–50 ml of fluid .The pericardial fluid volume is determined by the equilibrium between production and drainage. Pericardial fluid is derived by plasma ultrafiltration through the epicardial capillaries (and probably the parietal’s pericardium), as well as a small amount of interstitial fluid from the underlying myocardium, during the cardiac circle. The fluid drainage is mainly accomplished through the parietal pericardium lymphatic capillary bed.
Pericardial effusion is the accumulation of an excess amount of fluid and/or an abnormal character to fluid in the pericardial space between the heart and pericardium. Because of the limited amount of space in the pericardial cavity, fluid accumulation leads to an increased intrapericardial pressure which can negatively affect heart function. A pericardial effusion with pressure enough to adversely affect cardiac functions is called cardiac tamponade. Pericardial effusion usually results from a disturbed equilibrium between the production and re-absorption of pericardial fluid.
Postoperative pericardial effusion is a common finding after cardiac surgery. Most effusions are small, asymptomatic and inconsequential. it can persist or progress and ultimately proceed to cause life-threatening cardiac tamponade. with reported rates up to 4.7% of patients.