<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> <Ul> <Li> Mitral regurgitation - this is when one of the mitral valve leaflets that usually stop blood flowing from the left ventricle to the left atrium fails, allowing blood into the atria during systole . This means that the left atrium will be overfilled, leading to rapid ventricular filling when the mitral valve opens . </Li> <Li> Elevated left atrial and left ventricular filling pressures, usually a result of a stiffened and dilated left ventricle </Li> <Li> Ventricular septal defect - this is a hole in the wall between the two ventricles, which allows rapid filling from the other ventricle . </Li> </Ul>

Identify all of the statements that are accurate regarding an s3 heart sound