What is constrictive pericarditis?

Pericarditis: Constrictive pericarditis involves stiffening/thickening/hardening of the pericardium or "heart sack". This can be caused by many disease processes. Constrictive pericarditis results in restricting the filling of the heart which in turn may cause shortness of breath, swelling etc..

Fibrosis and scar: The heart is wrapped in a double layer of thick fibrous tissue called the pericardium. Normally only a few drops of lubricating fluid is present in this potential space. Following an infection or radiation or trauma (or a few other causes), the two surfaces scar down and don't allow the heart to fill with blood during diastole which "constricts" it and causes a form of congestive heart failure.