Inflamed heart sac. Gross specimen of a heart sac (pericardium) that has the abnormal presence of fibrin protein on its surface, giving it a rough appearance. This type of pericarditis (heart sac inflammation) is called fibrinous pericarditis. Pericarditis is usually caused by bacterial, viral or fungal infection, an injury, cancer, a heart attack or an autoimmune disorder. The treatment depends upon the cause, though anti-inflammatory drugs usually relieve the symptoms.