Background: The heart is essentially a pump. In warm-blooded mammals, there are two pumps to increase the blood flow when it drops in the capillaries of the lungs to present a large surface area for gas exchange. The heart is needed for aerobic respiration and it can be found in the thoratic cavity.
Difference of the sides The left side of the heart (right on the diagram) deals with oxygenated blood from the lungs while the right side (left on the diagram) deals with deoxygenated blood from the rest of the body.
Atrium (top chamber) and vesicle (bottom chamber) There are two chambers in each side of the heart called the atrium and the vesicle. The atrium's function is to pump blood to the vesicle so it only has a thin muscular wall but the vesicle's function is to pump blood to the rest of the body so it has a thicker muscular wall.