The clinical diagnosis of typical cardiac insufficiency with all the signs of congestive phenomena, as a rule, present no difficulties; but with the appearance of these grave manifestations the prognosis is, as a rule, dubious. As within so many fields in modern medicine, an early diagnosis is striven for so that by means of restrictive measures the breaking down of the vital functions of an organ may be delayed as far as is possible or sometimes even prevented. To arrive at this early diagnosis it is necessary in many cases to make use of functional tests which by increasing the load on the organ aims at elucidating the functions of that organ; in other words, a functional diagnosis. There have been abundant opportunities to experience the great importance of this; for example, in the case of the ventricle, kidneys, pancreas and biliary tract. In the case of the heart