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Heart. Historical illustration of the chambers of the heart. Deoxygenated blood enters the heart's right side (top) through the two vena cavae (blue, upper left). From the right atrium (upper left) blood passes to the right ventricle (upper centre) which contracts and pumps blood into the pulmonary artery (blue, upper right) and to the lungs. This is repeated in the heart's left side (bottom), which pumps oxygenated blood from the pulmonary veins (red) into the aorta (orange) and around the body. A cross-section through the ventricles is at centre left. Two views of a foetal heart at 8 months are at centre right. Colour lithograph by Fairland from The Viscera of the Human Body, 1840. (KEYSTONE/SCIENCE PHOTO LIBRARY/SHEILA TERRY)