An illustrated cross section of the heart showing deoxygenated blood (blue) and oxygenated blood (red) traveling through the heart. Deoxygenated blood enters the right atrium, passing through the tricuspid valve into the right ventricle. Blood travels to the lungs via the pulmonary arteries and back to the left atrium via the pulmonary veins. Passing through mitral valve, the left ventricle pumps the oxygenated blood into the aorta to supply the entire body.