The right side and left side of the heart are separated to prevent the mixing of Oxygen and deoxygenated blood in vertebrates. Blood goes through the heart twice during each cycle this defined as double circulation. The muscle in the heart are known as cardiac muscles. All the muscles contract and relax. As they move at appropriate time and make heart behave like a pump. Pressure of blood inside the artery during ventricular contraction is known as systolic pressure, where the pressure in the artery during ventricular relaxation is known as the diastolic pressure.

Artery

They carry blood away from the heart. They carry oxygenated blood except the Pulmonary artery they have thick walls.

Veins

They carry deoxygenated blood except Pulmonary vein. They have thin walls and also poses valve they carry blood towards the heart.

Capillaries

They are extremely thin vessels which connect arteries to veins. Through these exchange of material take place.

The ventricles have thick wall which prevent the back flow of blood and spread blood to all the part of the body are known as volve.

This process goes like from lungs the oxygenated blood goes to the upper left Atrium through the Pulmonary vein. From left Atrium the blood goes to the lower left ventricle and from the left ventricle the blood goes to the body parts through arota ( artery ) and from the Body the deoxygenated blood goes to the upper right Atrium through supirior venacava ( vein ). From the upper right Atrium the blood goes to the lower right ventricle and from the right ventricle the blood goes to the lungs back again through the Pulmonary artery.