Following hea sound is almost Pathological;
Fouh Hea Sound (S4) It is due to ventricular filling and cannot be heard even by a stethoscope since its frequency is below the audible limit (20 Hz). It is always pathological. It can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hyperophy. It is produced during last rapid filling of ventricles, which occurs due to atrial systole. Hence, it is also called "atrial sound".
S1
S2
S3
S4
FMGE 2019