Detection and treatment of pericarditis remains a challenging problem and the etiology is unknown in 40–85% of cases. As a result, a large proportion of cases are labeled idiopathic pericarditis. The advent of echocardiography, an accurate noninvasive method for the detection of effusion, has clarified the definition from pericarditis to pericardial effusion, which is a standardized and clear entity. A systematic approach to diagnostic testing based on standardized practice guidelines has been proposed. This strategy has led to a decrease in the number of cases classified as idiopathic and to the identification of treatable conditions. Percutaneous pericardiocentesis, guided by fluoroscopy or echocardiography, can now be carried out safely and rapidly and has also allowed the intrapericardial instillation of drugs, representing a new treatment strategy. The inclusion of flexible pericardioscopy, immunohistochemistry and contemporary molecular biology tools has improved the diagnostic value of the biopsy.