Pericarditis is a common but frequently subclinical entity. There are a number of causes, including infection, systemic illness, cardiac disease, trauma, and neoplasm. Iatrogenic causes include surgery, cardiac instrumentation, irradiation, and medications. The clinical presentation varies, depending on the cause. Chest pain and dyspnea are characteristic complaints. A typical progression of ECG changes occurs during the course of acute pericarditis. These changes occasionally require differentiation from those of acute myocardial infarction or normal variant ST segment elevation. Echocardiography is the most sensitive technique for detecting the presence of pericardial effusion. In addition, a number of echocardiographic findings are characteristic of larger effusions and cardiac tamponade. Any form of pericarditis may lead to the development of cardiac tamponade. Malignant effusion is probably the most common single cause.