Inflamed heart sac. Light micrograph of a section through tissue from a heart sac (pericardium) in a case of pericarditis (heart sac inflammation). The tissue also shows signs of neoplasticity and this is termed neoplastic pericarditis. Neoplasticity is new and abnormal growth, and can turn cancerous (malignant). Pericarditis can be caused by fungal, viral or bacterial infection, an injury, cancer, a heart attack, or an autoimmune disorder. Treatment depends on the cause, though anti-inflammatory drugs usually relieve the symptoms. Magnification unknown.