Acute pericarditis is usually a benign self-limiting condition, often of unexplained or viral aetiology, involving inflammation of the pericardial layers. It is often part of the differential diagnosis in patients admitted with acute chest pain and can be confused with acute myocardial infarction, acute pulmonary embolism and pleurisy. Occasionally it can result in cardiac tamponade and, if associated with myocarditis, in heart failure. This article sets out how to diagnose acute pericarditis, the common underlying causes, the possible treatment options and outcomes.