There is need of a practical method of determining the condition of the heart muscle in man. The contraction period of other muscles is lengthened if they are fatigued or degenerated, and this may be true of heart muscle. An accurate determination of the length of systole might be of use, provided its normal relationship to the heart rate and the ordinary variations were known.At the Minneapolis meeting of the American Physiological Society December 28, 1917, the writers reported that they had studied the length of systole and diastole in man, by recording the carotid pulse and measuring the systole from the beginning of the upstroke to the dicrotic notch. The subjects were 20 normal men, and 1,600 cycles were measured. A curve in which the average duration of systole and of diastole were plotted in relation to pulse gave a striking picture of the shortening of systole and diastole by increasing heart rate.The great variation in the length of systole and diastole which may occur within a single minute was...