Split First and Second Heart Sounds


In the normal heart: During expiration:The second sound (S2) is usually single During inspiration: The second sound (S2) is made of two component sounds: Aortic valve closure (A2) which happens first.Pulmonic valve closure (P2) which happens second. A2 is heard widely all over the chest.  So when you hear 'S2' at the mitral area, you are really hearing A2. Normally, P2 is soft and only heard at the pulmonic region (left parasternal, intercostal space 2), however even in this region A2 is louder. There are believed to be multiple causes for the physiologic splitting of S2. Both A2 and P2 close when the pressure above the respective valves are greater than the pressure in the ventricles below. Given the lower vascular resistance of the pulmonary artery, during inspiration, the pulmonary artery is able to tolerate more volume of blood before the pressure above the valve increases. Additionally, during inspiration, more blood fills the right ventricle leading to a slightly longer ejection time, adding to the delayed pulmonic valve closure.
Split First and Split Second HS
Unsplit First and Second HS

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