3. Heart sound: S1, s2, S3, S4 SI: S indicates the beginning of the ventricular constraction 1)Vibration of the closure ofA-v valve 2)Opening of the semilunar valve 3) Acceleration of the blood in arteries3. Heart sound: S1 , S2 , S3 , S4 • S1 : S1 indicates the beginning of the ventricular constraction 1) Vibration of the closure of A-V valve 2) Opening of the semilunar valve 3) Acceleration of the blood in arteries