Directly underneath the pulmonary arteries, which send deoxygenated blood to the lungs, are the pulmonary veins, which channel oxygenated blood from the lungs back to the heart. Blood enters the left atrium from right and left pulmonary veins and then passes through the mitral valve into the left ventricle. From there, it is pushed through the aortic valve into the large aorta. The aorta passes under the main pulmonary artery, arches over the left atrium, and then travels down the rear of the heart, taking oxygen-rich blood to the legs and internal organs. From the top of the aortic arch, three arteries—the brachiocephalic artery, the left cartoid artery, and the left subclavian artery—branch off to bring oxygenated blood to the head and arms.