In referring to the various disorders of the pericardium, one is accustomed to use such terms as pericarditis with effusion, adhesive pericarditis, callous pericarditis, purulent pericarditis, hydropericardium, hemopericardium and pneumopericardium. These anatomic conditions, diversified as they are, have a common physiologic relationship. They produce two closely related clinical syndromes. These are the syndromes of acute and chronic intrapericardial pressure. It is our purpose to describe these clinical syndromes and recommend the adoption of this physiologic concept. We believe this would aid in the diagnosis of pericardial lesions in much the same way as the physiologic conception of intracranial disorders has aided in the diagnosis of intracranial lesions. The syndromes of acute and chronic intracranial pressure are well understood and their physiologic aspects have been of great importance in furnishing the guide to specific anatomic diagnoses. For example, a patient who is unconscious, with Cheyne-Stokes respiration, a high blood pressure, a