Which of the following is true about fourth heart sound `S4'
Fourth heart sound occurs due to the late rapid filling phase of the ventricle, which occurs due to atrial systole. Since its frequency is usually less than 20Hz, it is not heard by an unaided ear.
Can be heard by the unaided ear
Frequency is greater than 20 Hz
Heard during ventricular filling phase
Heard during ventricular ejection phase