Following steps are included in the flow of blood through the heart of human beings:

(i) The pulmonary vein brings the oxygenated blood from the lungs in the left atrium of the heart.

(ii) Left atrium contracts and pumps blood into the left ventricle through valve.

(iii) When the left ventricle contracts, the oxygenated blood enters the main artery called aorta. The blood travels from the main artery to larger and smaller arteries into the capillary network.

(iv) The aorta transports the blood to all the organs of the body except the lungs. The oxygenated blood releases oxygen, nutrients and other substances and takes on carbon dioxide and waste substances. The deoxygenated blood enters the vena cava which carry it to the right atrium of the heart.

(v) Right atrium pumps deoxygenated blood into the right ventricle through the valve.

(vi) When the right ventricle contracts, the deoxygenated blood enters the lungs through pulmonary artery and releases carbon dioxide and absorbs fresh oxygen from air. The blood becomes oxygenated again and is sent to the left atrium of heart by pulmonary vein for circulation in the body. This whole process is repeated continuously.