Heart sounds

  • With each heart-beat, the detectable heart sounds are produced.
  • These sounds represent the auscultatory events of the cardiac cycle.
  • Heart sounds can be amplified and recorded by placing an electronically amplified microphone on the chest.
  • The recording of such sounds is called a phonocardiogram.
  • There are four heart sounds associated with the cardiac cycle.
  • Among them only the first and second heart sounds (traditionally referred to as lubb and dupp, respectively) can be heard easily with a stethoscope.

First heart sound

  • It is more complex, lower in pitch and lasts longer than the second sound.
  • It occurs as a result of the ventricles contracting which forces blood against auriculo-ventricular valves.
  • This causes them to bulge backward towards the atria until the chordae tendinae abruptly stop the bulging.
  • The elastic nature of the valves then causes the blood to bounce forward into each ventricle.
  • This causes the blood, ventricular walls and valves to vibrate.
  • It is these vibrations that produce the first heart sound.

Second heart sound

  • It is high in pitch.
  • It results from the sudden closing of the semilunar valves.
  • This allows them to bulge backward towards the ventricles until their elastic stretch recoils the blood back into the arteries.
  • This recoil produces vibrations that reverberate back and froth between the heart walls, arteries and valves.
  • When the vibrations contact the chest wall, they create what can be heard as the second heart sound.
  • The second heart sound is heard best over the second inter-costals space, where the aorta is closest to the surface.
  • Immediately after the second sound there is a short interval of silence.

Third heart sound

  • It is a low-pitched sound which is heard occasionally.
  • It is caused by the vibration of the ventricular walls after the atrio-ventricular valves open and the blood pushes into the ventricle.
  • This sound is heard best in the tricuspid area.

Fourth heart sound

  • It is usually not heard with an unamplified stethoscope in normal heart.
  • It is caused by the blood rushing into the ventricles.
  • Heart sounds are important tools in diagnosing valvular abnormalities.
  • Any unusual sound is called murmur.

Heart sounds

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