Light micrograph of a human heart tissue section showing fibrinous pericarditis. The pericardium is a fluid-filled double-walled membrane sac that surrounds the heart. The fluid is separated by two layers, the fibrous and serous pericardium. The fibrous pericardium is the outer layer and holds the heart in place and protect it from surrounding infections. It is composed of thick connective tissue. Fibrinous pericarditis is usually caused by trauma, acute myocardial infarction, uraemia, collagen and vascular disorders. The pericardium can develop an inflammatory process for a variety of reasons.