The heart, as the central organ of our circular system, is the center of two series-connected circulations. The big circulatory system begins in the left ventricle of the heart. From there, the oxygenated blood is first pumped through contractions into the aorta, then into the following arteries or arterioles, and finally into the capillaries of the body. The blood proceeds to flow from the capillary bed to the venules, veins, and reaches via the superior and inferior venae cavae the right atrium of the heart. The pulmonary circulation begins in the right ventricle of the heart. From there on, desoxygenated blood is pumped through the pulmonary arteries into the pulmonary capillaries. From the capillary bed of the lung it arrives in the left atrium of the heart and can begin its journey in the big circulation again. The heart is supplied by the coronary arteries.