The pathogenesis of heart failure in rheumatic cardiac disease is a subject of some controversy. The discussion centers about the influence of two general causes of failure: first, that of some infectious process, and second, that of a mechanical factor, exertional strain. Although clinical observations seem to indicate that the infectious element is decidedly the more important,1the exact nature of the infection has not been adequately determined. The present investigation was undertaken to clarify this point further.2 The clinical material reviewed for this study included 100 consecutive cases of uncomplicated rheumatic cardiac disease with heart failure, studied in the wards of the Presbyterian Hospital prior to 1932; 75 cases of rheumatic cardiac disease and heart failure with autopsy, and 50 clinical cases of syphilitic cardiac disease with decompensation. The history, results of physical and laboratory examination and postmortem observations have been studied to determine, if possible, the