The third heart sound or S3 is a rare extra heart sound that occurs soon after the normal two heart sounds S1 and S2.
The third sound occurs at the beginning of diastole approximately 0.12 to 0.18 seconds after S2.
S3 may be normal in people under 40 years of age and some trained athletes but should disappear before middle age.
This sound late in life is abnormal and may indicate serious problems like heart failure.
S3 is of lower in pitch than the normal sounds
S3 best heard with the bell of the stethoscope.
Best heardat thr cardiac apex with the patient lying in the left lateral decubitus position.
Ref2242ed to as a ventricular gallop or a protodiastolic gallop because of its place in early diastole.
It is a type of gallop rhythm as the S4 gallop.
When S3 and S4 gallop occur together forming a quadruple gallop.
With tachycardia it is difficult to distinguish between S3 and S4 thus producing a single sound called a summation gallop.
S3 heart sound when present in a child or young adult implies the presence of a supple ventricle that can undergo rapid filling.
In a middle-aged or older adult, an S3 is often a sign of disease, indicating increased ventricular filling due to congestive heart failure or severe mitral or tricuspid regurgitation.
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.
S3 occurs until the middle third of diastole when the ventricles are filled sufficiently to create enough tension for reverberation.
S3 may occur as a result of tensing of the chordae tendineae during rapid filling and expansion of the ventricle.
It is associated with heart failure, caused by conditions with rapid ventricular filling such as mitral regurgitation, in the presence of elevated left atrial and left ventricular filling pressures, usually a result of a stiffened and dilated left ventricle ventricular septal defect, post myocardial infarction, dilated cardiomyopathy, tricuspid regurgitation, hypertensive heart disease.
The condition itself does not need to be treated, but rather the underlying cause requires correction. Depending on the aetiology the gallop rhythm may resolve spontaneously.
Pathologic after the age of 40 years, and is produced by diastolic vibrations of the left ventricular wall that accompany rapid ventricular filling.
Often considered a sign of heart failure or reduced ventricular function.