Blood flows through veins into the heart’s upper chambers (atria) and is pumped into the arteries by the lower chambers (ventricles). Deoxygenated blood collects in the right atrium and flows into the right ventricle, which pumps it to the lungs. Oxygenated blood returns from the lungs to the left atrium. The left ventricle then pumps this blood around the body.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.