Acute pericarditis may be of viral or idiopathic origin, may be induced by certain drugs, may occur as a consequence of thoracic surgery, may result from infection by bacteria or other organisms, or may be associated with noninfectious systemic disease. In some instances, pericarditis may be detected quickly, and in other cases it may not be recognized until late. This article discusses clinical findings, clinical course, and treatment of acute pericarditis. In addition, diagnosis and treatment of pericardial effusion are presented.