<P> S may be normal in people under 40 years of age and some trained athletes but should disappear before middle age . Re-emergence of this sound late in life is abnormal and may indicate serious problems like heart failure . The sound of S is lower in pitch than the normal sounds, usually faint, and best heard with the bell of the stethoscope . </P> <P> It has also been termed a ventricular gallop or a protodiastolic gallop because of its place in early diastole . It is a type of gallop rhythm by virtue of having an extra sound; the other gallop rhythm is called S . The two are quite different, but they may sometimes occur together forming a quadruple gallop . If the heart rate is also very fast (tachycardia), it can become difficult to distinguish between S and S thus producing a single sound called a summation gallop . S is a dull, low - pitched sound best heard with the bell placed over the cardiac apex with the patient lying in the left lateral decubitus position . This heart sound when present in a child or young adult implies the presence of a supple ventricle that can undergo rapid filling . Conversely, when heard in a middle - aged or older adult, an S is often a sign of disease, indicating increased ventricular filling due to congestive heart failure or severe mitral or tricuspid regurgitation . </P> <P> S is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by the inflow of blood from the atria . The reason the third heart sound does not occur until the middle third of diastole is probably that, during the early part of diastole, the ventricles are not filled sufficiently to create enough tension for reverberation . It may also be a result of tensing of the chordae tendineae during rapid filling and expansion of the ventricle . </P> <P> It is associated with heart failure, caused by conditions which have: </P>

What is the cause of s3 heart sound
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