The first heart sound is the manifestation of heart contraction, the second heart sound is the manifestation of ventricular diastole, the specific causes are as follows.
1. The first heart sound: the first heart sound is mainly due to the pressure difference generated during ventricular contraction, under which the closure of the atrioventricular valve and the effect of blood flow on the atrioventricular valve will cause the ventricle to vibrate, or vibration generated by the effect of the blood emitted from the ventricle on the wall of the veins. The vibration is lower in pitch but longer in duration.
2. Second heart sound: It is the pressure difference formed during the diastolic phase of the ventricle, which causes the aortic valve to close or causes the pulmonary valve to close, and vibrates when the blood impinges on the root of the aorta. This vibration is relatively high in pitch and relatively short in duration.
The first and second heart sounds can be detected by auscultation.