In the examination of the heart, various methods are employed. Most of them are of value, but none of them afford an accurate index as to the functional capacity of the heart. The most commonly employed method of estimating the functional capacity consists in counting the pulse before and after standardized exercise. Concerning such tests, Sir James Mackenzie1stated: One of the most profitless lines of investigation has been those numerous and elaborate attempts to discover the condition of the heart's efficiency by various tests in which bodily effort is employed and the heart rate taken as a standard. With regard to the measurement of cardiac capacity for work, Sir Thomas Lewis2said: Innumerable tests have been, and continue to be devised to answer this question; they are based mainly upon pulse and blood pressure readings . . . . Experience of such tests have convinced me that they have little practical