The structure of the Heart

The heart is a powerful muscle known as the Myocardium. The heart has two separate pumps that continuously send blood throughout the body carrying nutrients, oxygen and removing harmful wastes.
The right hand side of the heart receives blood low in oxygen and the left side receives blood that has been oxygenated by the lungs.

Right Atrium

The right atrium is larger than the left side as it receives blood back from all the other parts of the body. The walls of the right atrium are thinner than the left as the blood it receives is under less pressure. It has two main veins that return the blood, theses are known as the superior vena cava and the inferior vena cava. The superior vein returns deoxygenated blood from the top half of the body and the inferior returns deoxygenated blood from the lower half of the body.
The right atrium also receives blood back from the heart itself. When blood is collected in the right atrium, it is pumped into the right ventricle through the tricuspid valve.

Left Atrium

The left atrium receives blood from four pulmonary veins. The blood has been oxygenated by the lungs. This blood is then pumped into the into the left ventricle through the bicuspid valve.

Right Ventricle

The right ventricle recieves blood from the right atrium. As the heart contracts blood is forced out through the pulmonary semilunar valve into the pulmonary artery.

Left Ventricle

The walls of the left ventricle are four times thicker than the right hand side. This is because the oxygenated blood it receives needs to be pumped to the rest of the body. When the heart contracts blood is forced through the aortic semilunar valve and into the aorta.

Aorta

The aorta is the largest vessel in the body. It carries oxygenated blood to every part of the body. It receives blood from the left ventricle.

Superior Vena Cava

This is one of the largest veins in the body. It returns deoxygenated blood to the right atrium from the upper parts of the body.

Inferior Vena Cava

This returns deoxygenated blood from the lower parts of the body to the right atrium.

Pulmonary Arteries

These carry blood from right ventricle to both of the lungs, where it is oxygenated and sent back to the left atrium of the heart.

Pulmonary Veins

These carry oxygenated blood back to left atrium in the heart.