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Third heart sound

S3 is a low pitched sound produced due to rapid deceleration of blood during inflow Into the leftventricle.It is also called as protodiastolic sound or ventricular gallop.S3 signifies diastolic overload of the ventricles. It occurs during the first rapid filling phase of cardiac cycle (in ventricular diastole).
Mechanism of S3 
More than normal amount of blood reaching the ventricle during rapid filling phase, produce stretch on myocardium - tense chordae and papillary muscle, it will produce S3
Pathogenesis of S3
Abnormally increased LVEDV due to increased transvalvular flow or diminished LV function.
Characteristics of S3

  • Low pitched sound
  • 0.12 sec after S2 in produced both in LV and RV

Physiological 3rd heart sound seen in children and adults upto 30 - 35 yrs.
Physiologic S3 is associated with functional murmur and venous hum and it disappears in standing position
What are the association of S3?
S3 commonly associated with the following

  • Pulsus alternans 
  • Narrow pulse pressure
  • Heaving apex
  • Other signs of LV/RV failure