Under normal conditions, the pericardial sac contains a small amount of fluid, varying in quantity from 10 to 50 cc. The fluid is clear and light amber in color. In the presence of disease of the pericardium, or of congestive heart failure, the pericardial fluid may become altered in character and increased in amount. The alterations in the organism in cases of pericarditis with effusion are of one, or both, of two sorts: (1) a mechanical handicap is imposed on the heart by the presence of considerable fluid, and (2) if the effusion is the result of pericardial infection, there is sepsis or toxemia. Pericardial effusion frequently is not recognized in life, and it has been stated that amounts of less than 150 cc. usually defy detection. This is, of course, not difficult to understand when one realizes the opportunity for concealment of fluid in the pericardial sac, if obstructing,