The pericardial cavity has been opened to reveal fibrinous adhesions between epicardium and pericardium in the top panel. There is also a small amount of reddish discoloration from hemorrhage. The shaggy fibrin is seen over the anterior surface of the heart in the lower panel. This is pericarditis. The etiology in this case was infectious (viral). A serous pericarditis, in which there is some inflammation but little or no exudation, is most often due to autoimmune diseases or viral infection. A fibrinous pericarditis can be localized over an area of myocardial infarctiion and more extensive when uremia is present. Fibrinous exudate may be present with infections and autoimmune diseases. Metastatic tumor and tuberculosis are most likely to produce extensive hemorrhage, often superimposed upon a fibrinous exudate. A purulent pericarditis is most often the result of spread of bacterial infection from lung or mediastinum. Healing of pericarditis most often results in focal adhesions, but occasionally (and particularly with tuberculous pericarditis) healing leads to extensie scarring that encases the heart ('constrictive pericarditis').