At operation the hemodynamics of the left side of the heart were studied in six patients without mitral stenosis, and in eight patients with mitral stenosis, by means of simultaneous needle puncture of the left atrium, left ventricle, and aorta. This technic permits analysis of the various phases of the cardiac cycale in normal subjects and in patients with mitral stenosis. The fundamental hemo-(lynamic expression of mitral stenosis is the presence of an elevated left atrioventricular filling pressure gradient, which ranged from 4 to 20 mm.Hg, and after valvulotomy fell in relation to the adequacy of the procedure.O UR knowledge of the human cardiac cycle has been retarded by the inability to study completely the hemodynamics of the left side of the heart. The technique of venous catheterization, which has contributed so much to an analysis of events in the right side of the heart of man1-3 does not permit the direct study of the left heart chambers except in isolated instances of congenital communications between the right and left cavities.Previous investigation of the left side of the circulation has been carried out primarily through animal experimentation.

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