Auscultatory findings of mitral stenosis is the most common question asked in clinical cardiology right from first clinical year to higher specialty examinations . It should be answered in a systematic way.
What happens to the murmur and sounds in mitral stenosis after the onset of AF ? When I asked this question in my class , many struggled . Hence this post .
* Correction
The A2-OS interval in critical MS is relatively short and only is minimal variation is expected in spite of AF .This is because, A2-OS interval is primarily determined by instantaneous LA pressure at the beginning of MV opening which is always high and does not vary much with RR interval .
Reference
Dr.S.Venkatesan MD 
Thank you so much With kindest regards