The blood comes in the ventricles because of the contraction in the atriums (atria) and the atrioventricular orifice gets closed. From this moment, the pressure of the blood gets increased in the ventricles because of filling blood and contraction starts in them. Semilunar valves on the mouth of arteries get open and the blood is pushed in them by pumping. There is contraction in both ventricles at one time. The apex of heart clashes with the walls of chest as the ventricles get contracted. This sound is felt by us as heart beat. It can be heard by keeping hand on the 5th intercostal space and 3¼ left side from the middle of the sternum. Just after it, AAKUNCHAN of atria starts. In a healthy person, the heart beats from 72 to 75 times in a minute. It is called heart beat. The heart beat can be less or more. In each heart beat, first both atrias contract and then both ventricles contract. Again both get loose at one time. This activity remains continue throughout life.
The heart beat is very fast in children. The rate of heart beat depends on the age, physical posture, mental and physical condition of a person. The rate of heart beat starts to decrease as a person grows older. The rate of heart beat becomes fast in some conditions of disease and at the time of exercise and emotional.
The process of cardiac muscles’ contraction which takes place first in the atriums and then ventricles is called systole and this process takes the time of 0.4 second. Thereafter, it is the time to take rest for the heart and there is no kind of AAKUNCHAN in this period viz both atrium and ventricle become loose. This period of rest is called diastole and this stage remains till four seconds. Because of meeting of both these, one cardiac cycle gets completed by meeting both these in which 8 seconds pass.