This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Fouh hea sound is caused by: March 2013 
Select and explain. 
A. Closure of the aoic and pulmonary valves, B. Vibrations in the ventricular wall during systole, C. Ventricular filling, D. Closure of the mitral and tricuspid valves
C: Ventricular filling
Answer: C: Ventricular filling 
Explanation: Ans. C i.e. Ventricular fillingFouh hea soundThe S4 sound occurs, by definition, immediately before S1, while the atria of the hea are vigorously contracting.It is manifest as a vibration of 20 to 30 Hz within the ventricle.While the mechanism is not absolutely ceain, it is generally accepted that S4 is caused by stiffening of the walls of the ventricles (usually the left), which produces abnormally turbulent flow as the atria contract to force blood into the ventricle.