In which circumstance might S4 be heard in adults?

S4, also known as a "gallop" sound, is produced due to the vibration of the ventricular walls resulting from atrial contraction. It often indicates a stiff or hypertrophied ventricle, which can occur in several circumstances.

In many adults with sinus rhythms, especially older adults, S4 can be a common finding. This may be associated with age-related changes in the heart, particularly left ventricular hypertrophy or decreased compliance of the ventricular walls, which are frequent phenomena in the aging population. Thus, the presence of S4 in adults with a normal sinus rhythm can reflect a physiological adaptation rather than a pathological condition.

While S4 may sometimes be heard in patients with conditions such as atrial fibrillation or bradycardia, it is not confined to these scenarios. In individuals with atrial fibrillation, for instance, the atrial contraction might not effectively contribute to S4 due to the irregular rhythm. Therefore, the occurrence of S4 is more commonly acknowledged among those with a consistent sinus rhythm who may exhibit signs of ventricular stiffness or hypertrophy as they age.