In which population is S3 considered a normal finding?

The presence of a third heart sound, known as S3, can be a normal finding in certain populations. In children and young adults, the heart is often more compliant, and the rapid filling of the ventricles during early diastole can produce this sound. It results from the sudden deceleration of blood flow into the left ventricle, especially during the rapid filling phase.

In contrast, in adults over 50, S3 can indicate heart failure or volume overload, as the compliance of the ventricle decreases with age. While S3 may appear in newborns, it is primarily attributed to the transitional physiology as the newborn adapts from fetal to extrauterine life. Hence, S3 is not typically classified as a finding that is normal for the entire adult population. In individuals with heart failure, the presence of S3 is often associated with pathology rather than normal physiology. Therefore, children and young adults represent the population where S3 can typically be considered a normal finding without alarm.