The heart is a large muscular organ. It is located in the middle of the chest area. The vessels leading into the heart are the aorta, superior vena cava, pulmonary arteries and pulmonary vein. The entry and exit to different chambers of the heart are projected by valves: pulmonary valve, tricuspid valve, mitral valve, and aortic valve. The four chambers of the heart are the right atrium, left atrium, right ventricle, left ventricle and the inferior vena cava. The valves ensure that blood travels in one direction through the heart by preventing backflow. Two or three leaflets close off when the blood has passed through.
The mitral and aortic valves control the flow of oxygenated blood on the left side of the heart. The tricuspid and pulmonary valves control the passage of deoxygenated blood on the right. The atrium (left and right) are the two low pressure pumping chambers of the heart; they pump the blood to corresponding ventricle chambers. The coronary arteries supply the heart muscle with the oxygen and nutrients it needs. There are three main arteries. Two parts are on the left artery and one part on the right artery. The arteries are like pipes. They carry the blood outwards from the heart to the tissues. The veins carry blood on the return journey.