¶ S1
• pronounced in MS
• weak in MR/MP
¶ S2
weak in both AS and AR
¶ S3 (blood splash!)
• comes just after S2 (early diastole)
• lub-dub-‘dub’
• normal in children, young adults, athletes, pregnancy, fever
• abnormal in others
• cause:
large poorly contractile left ventricle usually due to volume overload
“blood from pulmonary veins forcefully hits the inside of the LARGE ventricle making this sound”. This is common in MR and AR.
¶ S4 (atrium contracts!)
• comes just before S1 (late diastole)
• ‘da’-lub-dub
• almost always abnormal
• cause:
left ventricle hypertrophy (not enlargement) due to an obstructive cause
“atrium forcefully contracts to get blood into the highly tense muscular ventricle”. It is common in HTN, AS, MS “late”, restrictive cardiomyopathy.
Medicopedia 
hello again, all the above information is kind of familiar to me cuz now in 2nd year i started the CV unit…
i just have a question to ask, what is your reference to the information you are giving us?
i mean is this from certain books, from the knowledge you acquired in med school, or from your clinical experience?
i am asking this so i can know if i can use this website as a reference…
thanx, and waiting for your reply.
I use various sources to get my information, my medical knowledge, the internet, Wikipedia, and well-known medical books. I don’t mention the sources because I modify a lot of the layout and add mnemonics and expressions that are my own. Expressions like “blood splash!” mentioned above is an example. Rest assured that every bit of information is double checked for accuracy. Moreover, every post (including illustrations) is original, in that it’s written by me or by my fellow authors, and is not found or taken from any other website.
Some of my illustrations are used in Wikipedia in medical pages. Check this post: https://medicopedia.wordpress.com/2009/03/11/renal-physiology-and-diuretics-revisited/