The left atrium is one of the four chambers of the heart. It is situated above the left ventricle, with which it is communicated by the mitral valve, and beside the right atrium, from which it is separated by the interatrial septum. The left atrium gets oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve. The left atrium is supplied mainly by the left circumflex coronary artery and is drained by the oblique vein of the left atrium. As the other three chambers, it is lined with endocardium, which is a serous membrane lining the four cavities of the heart.