Pericarditis is a disorder caused by inflammation of the pericardium, the thin,sac-like membrane that surrounds the heart. Pericarditis can be caused by bacterial, fungal, or viral infections. It may also result from vascular inflammation (vasculitis), kidney or thyroid diseases, tumors, and injury or trauma to the chest, esophagus, or heart. In many cases, the cause is unknown. Pain occurs as a result of the layers of the inflamed pericardium rubbing against each other.