The temporal relationships of the various waves of the ballistocardiogram have been studied by, means of simultaneously recorded electrocardiograms, femoral pulses, and electrokymograms of the great vessels and heart chambers. A modification of the Dock type of electromagnetic, undamped, direct ballistocardiograph has been employed in this study of 23 normal individuals. The total duration of mechanical systole in the great vessels has been found to correspond closely to the H-L interval. The HWJKL complex of the ballistocardiogram appears to be entirely related to the events of ventricular systole. The M, N and 0 waves represent after-waves occurring during diastole.H ENDERSON1 studied the recoil curves of the heart and circulation as early as 1905 and attempted to derive cardiac output. For many years, little was done with this method until Starr2 modified the apparatus and suggested its use not only for the measurement of cardiac output but also as a clinical tool in evaluation of the functional status of the heart. Starr and his co-workers extensively investigated ballistocardiography and described the findings in both health and disease. However, because of the bulkiness of the equipment, the method did not gain widespread clinical application until recently when Dock and Taubman3 described a simple, portable and easily constructed instrument which recorded the ballistic curve directly from the body.The origin and naming of the various waves of the ballistocardiogram was described by Starr With the advent of electrokymography in a stable, practical form,7 an excellent means of studying the temporal relationship of the ballis--tocardiogram to the events of the cardiac cycle was established. We have studied the relationship of the ballistocardiographic waves to the electrokymogram in the normal state.MATERIAL AND METHODS Twenty-three normal subjects ranging in age from 18 years to 38 years were selected. Ten were male and 13, female. The usual clinical criteria were used to judge these subjects normal: namely, history, physical examination, electrocardiogram, x-ray films. of the chest, urinalysis and hemogram. The studies were all carried out at the same time of the day, usually three hours after eating. No attempt was made to secure a strict basal state. The following four events were simultaneously recorded on a four-channel, direct-writing oscillograph, the characteristics of which have been described elsewhere8:(1) the electrocardiogram lead I, (2) electrokymogram, (3) ballistocardiogram, (4) femoral sphygmogram. All tracings were taken with the subject in the recumbent position and with the breath held in midinspiration. Electrokymograms were obtained in the postero-anterior projection. The following points were selected: (1) midportion of the aortic knob, (2) pulmonary artery at the left cardiac border, (3) high left ventricle, (4) left ventricle near the apex. All recordings were made at a paper speed of 25 mm. per second.The electrocardiogram was selected as the com-

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During the past 18 months more than 100 normal and abnormal subjects have been studied with this instrument in our laboratory, utilizing the recorded heart sounds, the carotid sphygmogram or the electrocardiogram as the primary points of time reference. We have been impressed with the inconstancy in the timing of the electrokymographic events obtained in ventricular tracings when studied with any of the above methods. The objections to each of these timing devices are well known. Thus, the factors of variability in the carotid sphygmogram which may be consequent upon variation of the rate of blood flow, elasticity and distensibility of the vessel have been discussed.' The validity of a comparison of the mechanical events in the cardiac cycle with the electrocardiogram has been called into question.7 The heart sounds represent a fusion of noises arising from both ventricles and are

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