Heart sounds comprise two main components: the first heart sound (S1), and the second heart sound (S2).7 This research analyzed the first heart sound, which expresses the function of the left ventricle.
The first heart sound is made by the closing of atrioventricular valves and is heard loudly in the apex; the second heart sound is made by the closing of the aortic valve and pulmonary valve and is heard loudly in the base of the heart.14 This experiment analyzed S1, but much research is being conducted on S2.15,16
In this experiment, the first heart sound showed a high correlation with changes in cardiac output.
The fact that the first heart sound has a correlation with cardiac output is very meaningful in various situations, and it is more significant given the fact that the heart rate can be deduced independently.
If the mitral valve cannot close properly due to disease or calcification, the first heart sound can be small or difficult to detect.