To devise a simple test for estimating the functional capacity of the heart has been the aim of many investigators for several years. Many tests were advanced, most of them based primarily on the response of the heart to exercise. The majority of these tests have proved of very little value and are not being used today. Within the past decade, the study of the vital capacity of the lungs as a functional test in heart disease has gained favor with many clinicians, and favorable reports on the use of this test have been made by Peabody and Wentworth,1 Ulrich and Nathanson2 and others. Peabody and Wentworth1 state that there is a definite relation between the vital capacity and the tendency to dyspnea, and have classified cardiac patients into four classes according to the heart's efficiency.
Patients with a vital capacity of 90 per cent, or more of the normal