The term "congestive heart failure" identifies a clinical syndrome characterized by at least three components: First, there is venous congestion of the pulmonary or systemic circulations, usually both but sometimes separately; second, there is usually retention of salt and water by the kidneys, resulting in edema, and, finally, these processes are causally linked with a failure of cardiac function. Restoration of cardiac compensation by measures which act directly on the heart, such as digitalis, often results not merely in improved cardiac function, as evidenced by a rise in cardiac output and a shrinkage in heart size, but also in the relief of venous congestion and the renal excretion of edema fluid. Although edema formation is a secondary consequence of cardiac failure, it has become increasingly apparent that the relief of edema by measures which have no direct effect on the heart may also eventuate not merely in a striking improvement