The heart can be thought of as the main pump within the circulation system. The right side of the heart collects blood returning to the heart from the body and pumps it through the lungs where the blood releases the carbon dioxide produced in the body and absorbs oxygen. From the lungs, blood flows back to the left side of the heart. The left side of the heart then pumps blood out to the circulation.

Figure 1: Location of the heart and lungs in the chest.

Figure 2: The lungs.

Figure 3: The pulmonary arteries and veins.