Third Heart Sound
When present, a third heart sound (S3) can be heard in early diastole, during the rapid filling phase of the ventricle after the opening of the atrioventricular valve. It is a dull, low-pitched sound, best heard in the tricuspid area.
Production of the S3 sound appears to be the result of the tensing of the chordae tendinae as rapid filling of the ventricles causes the chamber to expand.
The third heart sound is a normal finding in children and young adults, in which groups, the sound is indicative of a supple ventricle that can undergo normal rapid expansion in early diastole. Conversely, when heard in a middle-aged or older adult, the S3 sound is often a sign of disease. It can indicate volume overload owing to congestive heart failure, or the increased transvalvular flow that accompanies advanced mitral or tricuspid regurgitation. A pathologic S3 is normally referred to as a ventricular "gallop".
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