Recent advances in the study of pericardial disorders have opened new diagnostic windows to the heart through the pericardial sac, with the development of pericardioscopy and thoracoscopy. Specific diagnosis of inflammatory, postinflammatory, autoreactive, or neoplastic pericardial disease can now be made by epicardial and pericardial biopsy and by cytologic analysis of the pericardial fluid. In perimyocarditis, optically guided epicardial biopsy gives more disease-specific results than does endomyocardial biopsy in the same patients. For viral and tuberculous pericarditis, molecular techniques such as polymerase chain reaction and in situ hybridization are available. Immunologic characterization of lymphocytic cells and antibodies demonstrates increased reactivity in viral, autoimmune, and neoplastic disorders of the heart. Doppler echocardiographic features in tamponade are reviewed thoroughly. Advantages and problems of pericardectomy in constrictive disease are noted, and finally, a pragmatic clinical and scientific approach for improved diagnosis of pericardial diseases is outlined.