The heart is the central organ of our circulatory system runs two circles that are connected. The big blood circulation begins in the left ventricle. Oxygenated blood is pumped through contraction into the aorta, arteries, arterioles, and eventually in the capillaries of the body. From the capillaries the blood flows back into the venules and venes and ends up via the superior and inferior vena cava in the right atrium of the heart. The small blood circulation (also pulmonary circulation) starts in the right ventricle. Desoxygenated blood is pumped via pulmonary arteries into pulmonary capillaries. From the capillaries of the lung it enters the pulmonary veins to get to the left ventrical and can begin its journey in the big blood circulation again. The supply of the heart is executed by so-called coronary arteries.