"The physiological or so-called venous pulse consists of three positive and three negative waves, bearing a more or less definite relation to the events of the cardiac cycle, and having their origin in the various movements of the chambers and structures of the right heart. The first positive wave (_a_) is presystolic in time, and is due to the contraction of the auricle, causing a slowing of the venous current and producing a centrifugal wave through a sudden arrest of the inflowing blood. The second positive wave (_S_) is presystolic in time, and originates in the sudden projection of the tricuspid valve into the cavity of the auricle during the quick, incipient rise in the intraventricular pressure occurring in the protosystolic period. The third positive wave (_v_) occurs toward the end of ventricular systole. It consists of two lesser waves separated by a shallow notch. The factors entering into its formation are the relaxation of the papillary muscle at a time when the intraventricular is still higher than the intraauricular pressure, resulting in an upward movement of the tricuspid leaflets and a return of the auriculoventricular septum to its position of rest. "The first negative wave (between positive wave _a_ and _S_) is due to the relaxing auricle. The second negative wave (_Af_) occurs during the diastole of the auricle. It is due to the dilatation of its walls, to the displacement of the auriculoventricular septum toward the apex occurring at the time of ventricular systole, and to the pull of the papillary muscles on the tricuspid valve leaflets. The third negative wave (_Vf_) appears during ventricular diastole and in the common pause of the heart chambers. Its cause is found in the passage of the blood from the auricle into the ventricle. It is somewhat modified possibly by the continual ascent of the auriculoventricular septum and by a wave of stasis due to the accumulation of blood coming from the periphery." (Fig. 36.) [Illustration: Fig. 36.--Simultaneous tracings of the jugular and carotid pulses showing normal waves in the venous pulse and relation to carotid pulse. (After Bachmann.)] Hirschfelder has described another wave which he calls the "h" wave, which is due to the floating up of the tricuspid valve by the blood in the ventricle before the complete filling of the ventricle following the auricular systole. (Fig. 37.) [Illustration: Fig. 37.--Jugular and carotid tracing from a normal individual with a well-marked third heart sound showing a large "h" and a smaller pre-auricular wave "w." ? indicates a small wave in mid-diastole following the "h" wave, occasionally found though perhaps an artefact. (After Hirschfelder.)] =The Electrocardiogram=