Abstract A new instrument has been devised to test condition of heart grossly at autopsy, thus aiding in a more accurate way our conception of the degree of degeneration of the heart muscle. Histologic examination of sections of heart from the site of test corroborated the gross findings as to degree of myocardial degeneration. One hundred and forty-five cases were studied at autopsy, 78 males and 67 females. A much greater series of cases must be studied in order to ascertain the degree of degeneration in various types of diseases. It is suggested that slight myocardial degeneration be called grade 1 degeneration; moderate, grade 2; marked, grade 3; very marked degeneration, grade 4. Grades 3 and 4 myocardial degeneration can be assumed to be cases of primary cardiac death in the absence of marked pathology in the other vital organs (lung, brain, etc.). Average heart readings showed less myocardial degeneration in lobar pneumonia than in bronchopneumonia. This applied to the cases of bronchopneumonia which preceded cardiac failure and were not terminal bronchopneumonias on a pre-existing pulmonary congestion and edema. Average heart readings showed slight or very slight degeneration in pulmonary tuberculosis. The lowest myocardiometer readings, with the most marked degree of generalized myocardial degeneration with necrosis of heart muscle, were found in two cases of gas bacillus septicemia ( B. aerogenes capsulatus or B. welchii infection).