Cardiovascular system. Schematic artwork of the human circulatory system. The heart (centre) is a hollow muscle that pumps blood around the body. Deoxygenated blood from the body is carried into the right side of the heart (left) via the vena cava (blue, left). From here, the blood travels into the lungs via the pulmonary artery (blue, centre), where it is oxygenated. The blood is then carried into the left side of the heart (right) before travelling back into the body via the aorta (red, centre), where it can exchange oxygen for carbon dioxide and start the cycle all over again.