Heart

The **heart** centrally positioned between the lungs within the mediastinum. Roughly the size of a fist, it is broad at the top and tapers toward the base. The human heart has four chambers: each side, left and right, contains one atrium and one ventricle. The upper chambers, the right atrium and left atrium, function as receiving chambers, contracting to push blood into the lower chambers, the right and left ventricles. Blood flows from the right atrium into the right ventricle, where it is then pumped into the pulmonary circuit. In the pulmonary capillaries, gas exchange occurs, with oxygen entering the blood and carbon dioxide being released. Blood rich in oxygen and low in carbon dioxide then returns to the left atrium. From the left atrium, blood moves into the left ventricle, which pumps it into the systemic circuit. After exchange in the systemic capillaries, blood returns to the right atrium, completing the cycle. *LICENSES AND ATTRIBUTIONS CC licensed content, Shared previously, 3.1 Heart Anatomy, Authored by: OpenStax College. License: CC BY: Attribution. License Terms: Download for free at:http://cnx.org/contents/0QN1UvTH@2.19:Y5T_wVSC@4/Heart-Anatomy* ## Keywords heart vein artery veins chamber valve upper left inferior vena cava right pulmonary tricuspid aorta pericardium heart muscle