An evaluation of electrocardiographic tracings as an index of myocardial damage in survivors of subacute bacterial endocarditis was undertaken in a study of 76 fatal cases of the disease. Anatomic changes, present in all, included myocarditis, perivascular infiltration and fibrosis, Aschoff bodies, infarcts, and intravascular emboli. Electrocardiographic tracings revealed changes which could be attributed to myocardial impairment confirmed at autopsy. Variation of pattern in serial records, although not diagnostic of specific disease, indicated an active process within the myocardium. Correlation of the electrocardiographic tracings with pathologic changes was not complete, but was sufficiently close to demonstrate the diagnostic value of electrocardiograms.