Acute pericarditis is a clinical syndrome caused by inflammation of the pericardium and characterized by chest pain, a pericardial friction rub and electrocardiographic abnormalities. The first step is to establish whether the pericarditis is related to an underlying medical problem that requires specific therapy; for instance, uraemic pericarditis will require urgent dialysis. Acute idiopathic pericarditis is usually benign but may rapidly constrict or pursue a relapsing course before burning out. Late complications of pericarditis include pericardial fibrosis and/or calcification, resulting in constrictive pericarditis, or a mixture of both effusive and constrictive pericardial disease. Recurrent effusions may require the formation of a pericardial window, balloon pericardiotomy or the instillation of chemotherapeutic agents. Electrocardiogram changes can occur a few hours or days after the onset of pericardial pain and are characterized initially by concordant, concave ST segment elevation in all leads except leads aVR, V1 and sometimes V2.