The present study is one in a series designed to elucidate the genesis of the precordial motions. It is concerned with an attempt to learn whether low-frequency precordial tracings (kinetocardiograms [KCG]) can be utilized as an index to the time of onset of ejection and filling. A number of observers have published data concerning the time elapsing between the beginning of electrical excitation and the start of the pressure rise in the pulmonary artery and the aorta.1-3These studies indicate that the right and left ventricles begin to eject at approximately 0.08 and 0.10 second, respectively, after the onset of the QRS. Similar studies indicate that ventricular filling begins about 0.10 second after the beginning of the second heart sound.2Consequently, this study is concerned with precordial motions occurring at these particular times, in the hope that such events may afford information which can be readily and simply