Chronic constrictive pericarditis is a term applied to the condition which results when fibrous thickening of the pericardium interferes mechanically with the normal movements of the heart and blood. Nineteen patients with an undoubted diagnosis of constrictive pericarditis have been observed by us in the Vanderbilt University Hospital in Nashville and two patients with a similar diagnosis in the Peter Bent Brigham Hospital in Boston. Studies of these patients form the basis of this report. That the knowledge of constrictive pericarditis has a quite respectable antiquity is demonstrated by the following quotation from Chevers, 1 written in 1842: "The principal cause of dangerous symptoms appears to arise from the occurrence of gradual contraction in the layer of adhesive matter which has been deposited around the heart, compressing its muscular tissue, and embarrassing its systolic and diastolic movements, but more particularly the latter." Among others, Cohnheim 2 and later Volhard 3