STUDIES ON STARLING'S LAW OF THE HEART. III. OBSERVATIONS IN PATIENTS WITH MITRAL STENOSIS AND ATRIAL FIBRILLATION ON THE RELATIONSHIPS BETWEEN LEFT VENTRICULAR END-DIASTOLIC SEGMENT LENGTH, FILLING PRESSURE, AND THE CHARACTERISTICS OF VENTRICULAR CONTRACTION.

Although 45 years have now elapsed since Starling's Linacre lecture on the "Law of the Heart Beat" (1), considerable controversy is still centered around the question of the applicability of this fundamental principle to the human heart. In several investigations the Starling concept has been examined by attempts to reproduce in man those experiments on the Starling heart-lung preparation in which its responses to acute changes in venous return were studied (2-6). In most of these investigations no consistent relationship between the filling pressure on the right side of the heart and the cardiac output was apparent. In experiments on the intact dog (7), Rushmer, Smith and Franklin have shown that the augmentation of cardiac work which accompanies muscular exercise is not associated with an increase in left ventricular dimensions. These experiments, when taken together with the observations on man (2-6), have cast considerable doubt on the hypothesis that the Frank-Starling mechanism is involved in the regulation of cardiac performance. In the present investigation, portions of which have been presented in preliminary form elsewhere (8), attempts were made to examine, in a critical manner, the applicability of Starling's law of the heart to man. To accomplish this, it appeared necessary to relate the end-diastolic fiber length and the end-diastolic filling pressure to the characteristics of ventricular contraction under conditions in which substantial changes in ventricular filling take place. It also seemed desirable