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Phonocardiography originated in an attempt to time the occurrence of heart sounds in the cardiac cycle in relation to the mechanical activity of the heart, as recorded in the apex beat or in arterial pulsations. The method evolved from an era when the observer manually inserted a signal in a pulse tracing at the time he heard the sounds. Later, this was done by mechanical synchronous record, then by an electric signal produced by a telephone pickup which stimulated a frog muscle to contract, then by direct recording through a capillary electrometer, or string galvanometer, and finally by electron tube amplification. Low-inertia capsule and mirror with photographic recording were also used, as well as other ingenious variations. Present day phonocardiography has developed mainly through improved instrumentation with low-noise level amplifiers and satisfactory filters. Spectral phonocardiography is the most important advance. The value of phonocardiography in clinical work lies in its ability to record for objective analysis the transient sounds and murmurs to which the hearing mechanism of different observers adds or subtracts subjective variants. It has been most useful in timing and explaining heart sounds having abnormal componentsÂ¿split sounds, atrial sounds, opening snaps, and gallop rhythms. It is also valuable in the study of certain murmurs, particularly in mitral disease and congenital heart disease. It has contributed to teaching and has been a useful diagnostic aid prior to cardiac surgery.