Human heart. Coloured historical artwork of the structure of a healthy human heart and its blood vessels. The heart pumps blood through three circulatory systems. The heart's surface has veins (blue) and arteries (red) of the coronary (heart) system, which run along grooves (sulci). The pulmonary (lung) system takes blood to the lungs (for oxygenation) through the pulmonary arteries (blue, upper right) and back from the lungs in the pulmonary veins (not seen). The aorta (red, upper centre) and vena cava (blue, above aorta) carry blood to and from the body respectively in the systemic (throughout the body) system. Taken from a 19th century German illustration.