"The chief value of the recorded heart sound is the possibility of accurately timing its occurrence in relation to the events of the cardiac cycle." This is even truer to-day than when Lewis first stated it (1915), because methods for recording events in the cardiac cycle have become more precise. In spite of this, there is still lack of agreement on the origin of the heart sounds. The causes of the second heart sound have been clearly defined, but there is a divergence of opinion on the origin of the major components of the first heart sound. On auscultation in young people the first sound may be heard to be narrowly split at the lower left sternal border. This splitting is widest and therefore most easily heard at the end of expiration (Potain, 1866). The origin of these two components has been attributed by some to closure of the auriculo-ventricular valves followed by opening of the semilunar valves (Orias and Braun-Menendez, 1939;Rappaport and Sprague, 1942;Luisada et al., 1949;Nazzi et al., 1954). Others have suggested that it is due to asynchronism in contraction of the ventricles (Wolferth and Margolies, 1945), and so to closure of the mitral valve followed by closure of the tricuspid valve (Leatham, 1954). Much of the evidence for these views has been obtained by relating the components of the heart sounds to dynamic events in the cardiac cycle by the use of reference tracings. Phlebograms and indirect carotid artery tracings have been mainly used for this purpose but these have the disadvantage that an arbitrary time interval has to be allowed for pulse wave transmission when assessing results.The present investigation has been undertaken to study the nature of the first and second heart sounds and to relate their components to events in the cardiac cycle by the use of synchronous border electrokymograms. These tracings represent volume and positional changes of the heart chambers and the great vessels during the cardiac cycle. Positive waves indicate outward movement and negative waves indicate inward movement of the heart borders. These tracings have the advantage of eliminating the arbitrary time factor for pulse wave transmission. METHODSIn the first part of the investigation phonocardiograms were taken, using the Elmqvist sixchannel Klinik recorder, with three different frequency responses. These are designated high frequency, medium frequency, and low frequency according to the degree of attenuation of low frequency vibrations in each; the high and medium frequency tracings are similar to the logarithmic phonocardiogram of Rappaport and Sprague (1942) in their frequency response. Within the range of the heart sounds and murmurs the medium frequency channel has a pattern in its frequency response similar to the human audiogram; it thus represents the heart sounds as they are heard through the stethoscope. The low frequency tracings represent rather lower frequencies than are ordinarily heard through a stethoscope. Recordings were taken routinely from the apex, the fourth and second left intercosta...

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