The Second Heart Sound (S2)
The second heart sound is produced by
the closure of the aortic and pulmonic valves. The sound produced by the closure of the aortic valve is termed A2 and the sound produced by the closure of the pulmonic valve is termed P2. The A2 sound is normally much louder than the P2 due to higher pressures in the left side of the heart, thus A2 radiates to all cardiac listening posts (loudest at the right upper sternal border) and P2 is usually only heard at the left upper sternal border. The A2 sound is thus the main component of S2.