¶ 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.