A schwannoma arising from the dorsum of the pontomedullary junction and presenting as an exophytic mass in the fourth ventricle is described. A ventricular schwannoma has not previously been reported in the literature. The presenting clinical and radiographic features and the pathology of this tumor are summarized, and an explanation is sought for its unusual location.

A technique for complete extrinsic denervation of the heart by the ablation of neural structures in the mediastinum is described. The completeness of denervation was verified by direct electrical stimulation of the main vagal and sympathetic trunks. Total deple tion of myocardial catecholamines followed the procedure in chronic survivors. Animals prepared in this manner are useful in the study of the neurologically isolated heart and simulate this aspect of the problem of cardiac transplantation.

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) to make such observations with the heart functioning with a relatively constant level of circulating catecholamines and of sympathetic stimulation, in view of the importance of these factors on myocardial performance (9).When the inflow of blood into the left ventricle is not impeded, most of the filling of this chamber occurs during the first portion of diastole, i.e., during the so-called rapid filling phase (10). When the heart rate is slow, this phase of the cardiac cycle is not encroached upon, diastasis is present (11,12), and changes in the duration of diastole do not profoundly modify ventricular filling. In patients with mitral stenosis, the obstruction to left atrial emptying prevents the left ventricle from filling rapidly during early diastole (12). Accordingly, it might be anticipated that in patients with mitral stenosis, and irregular ventricular rates due to atrial fibrillation, at any given left atrial pressure, beat-to-beat variations in the filling of the left ventricle take place due to alterations in the duration of the filling period. It was considered that if Starling's law of the heart operated in patients with mitral stenosis, the characteristics of each left ventricular contraction should appear to be a function of the previous end-diastolic fiber length or end-diastolic pressure, i.e., beats evidencing a relatively great force of ventricular contraction should be preceded by greater enddiastolic fiber lengths and filling pressures than beats evidencing a relatively smaller force of ventricular contraction. On the other hand, if Starling's law did not operate in these patients, then no clear relationship should be evident between ventricular end-diastolic fiber length or end-diastolic pressure and the characteristics of the subsequent contraction. 1874

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