The bloodstream in the body can be simplified as follows: The left side of the heart is responsible for the blood support to all organs in the body. Oxygen-rich blood (color: bright red) is pumped from the left side of the heart across the main body blood vessel, the aorta, to all organs of the body via the smaller blood vessels, the arteries (systemic circulation). This is how all the organs are supplied with oxygen. After perfusion of the organs and the body, oxygen is used for energy supply. The now oxygen-poor blood (color: deep blue) enters the right side of the heart over the veins. From the right side the blood is pumped to the lungs (pulmonary circulation), where it is enriched with oxygen and heads back to the left side of the heart.