The direction of blood flow in the heart, venous blood collected from all over the body is taken in to the right atrium of the body, the right atrial blood of the heart flows through the tricuspid valve into the right ventricle, and through the contraction of the right ventricle the blood is ejected into the large pulmonary artery. The pulmonary artery blood is filtered through the circulation of the lungs, filtering the venous blood with lower oxygen content into arterial blood with higher oxygen content and lower carbon dioxide content, and the arterial, blood flows back into the left atrium through the pulmonary veins. The blood in the left atrium passes through the mitral valve into the left ventricle, which undergoes contraction, and after contraction ejects the arterial blood with sufficient oxygen content outside the body into the large arteries of the body. Therefore, the direction of blood flow in the heart is mainly from the right atrium to the right ventricle, passing through the pulmonary circulation and then flowing into the left atrium and then into the left ventricle, where it is ejected into the aorta.