Notwithstanding the insistence of many internists and the great interest in functional disturbances of the cardiac mechanism aroused by the information obtained from the use of the polygraph and electrocardiograph, there is still a marked tendency among physicians to stress unduly the importance of valve lesions of the heart. If one glances through the systems and textbooks of medicine, one gains the idea that various forms of valve lesions originating from chronic endocarditis form the chief cause of cardiac disease. The diagnosis and treatment of valve lesions bulk large in the chapters devoted to heart disease. Scattered through the pages there is ample evidence that in the last analysis, muscle function determines cardiac efficiency or inefficiency, and various forms of chronic degeneration and interstitial inflammation of heart muscle are described. There rarely appears, however, a clear description of a common type of chronic cardiac disorder in which the fault is