@Slashvi 25 June 2022 more from that month

WHY does the heart beat in pairs? These sounds are generated by different parts of the heart and different valves. The first beat is the sound of blood reverberating (reflecting) in the left atrium when the mitral (atrial-ventricular) valve closes. It marks the end of the pumping of a portion of blood from the atrium to the ventricle. The second beat is created by the reverberation of blood in the left ventricle at the closure of the ventriculo-aortic valve and signifies the end of the ejection of the blood portion into the aorta. In the right heart, the beats are weaker and therefore not audible.