Measurements have been made of total exchangeable sodium, total body potassium, and total body water in a group of 13 previously edematous patients with heart disease, and in 20 “control” patients. The data show that while both groups have the same quantity of water as the per cent of bodyweight and the same body potassium concentration, the cardiac group has an excess of exchangeable sodium when compared with the “controls.” Since the excess sodium in the cardiac group cannot be attributed to the loss of potassium or the accumulation of water, the results of these studies are taken as evidence that osmotic inactivation of a considerable amount of some cation, probably sodium, has taken place. It is suggested that a likely site for cation binding is in the polyanionic constituents of the connective tissues.