The second heart sound (S2) is created by the closing of the aortic valve followed by the closing of the pulmonic valve.
Careful analysis of the splitting and intensity of the second heart sound can indicate the presence of many cardiac abnormalities.
This example shows normal physiological splitting of the second heart sound. Splitting varies between zero and eighty milliseconds depending on the phase of the respiratory cycle.
The aortic component of S2 (S2A) preceeds the pulmonic component (S2P).