Briefly describe the working mechanism of the human heart.

Explanation

The circulation of blood in the body takes place due to the pumping action of the heart. The heart receives blood from the veins and pumps it into the arteries. This pumping action is caused by the alternate contraction and relaxation of the muscles of the heart.
During relaxation, both the atria (singular - atrium) get filled with blood. The left atrium gets filled with the oxygenated blood brought by pulmonary veins from the lungs while the right atrium with the deoxygenated blood brought by inferior vena cava and superior vena cava from different parts of the body.
When atria contract, the biscuspid and tricuspid valves open. As a result of this, the oxygenated blood enters from the left atrium into the left ventricle while deoxygenated blood from the right atrium enters into the right ventricle.
When the ventricles contract, the bicuspid and tricuspid valves get closed. Owing to this, the oxygenated blood from the left ventricle enters into the aorta which supplies it to different parts of the body through its branches, while the deoxygenated blood from the right ventricle is carried to the lungs through pulmonary artery for purification. From this, it is obvious that blood circulates in the body due to the pumping action of the heart.