• There are optimal recording sites for the various heart sounds.
• Heart sounds and murmurs have extremely small
amplitudes with frequencies from 0.1 to 2000 Hz.
• Thus the recording device must be carefully
selected for wide band frequency response
• Specially designed acoustically quiet environment is
needed for noise free recording of heart sounds.
• Mechanical stethoscopes amplifies sound because of Standing wave
• Firm application of the chest piece makes the diaphragm taut
with pressure thereby causing an attenuation of low frequencies.
• Loose-fitting earpiece cause leakage which reduces the coupling
between the chest wall and the ear.
• Electronics stethoscopes has selectable frequency response
characteristics ranging from “ideal” flat-response to selectable band-
• A Phonocardiogram is a recording of the heart sounds and
• Eliminates subjective interpretation of the heart sounds
• Enables evaluation of the heart sounds and murmurs with
respect to the electric and mechanical events in the cardiac
• Evaluation of the result is based on the basis of changes in
the wave shape and various timing parameters.