How the heart and circulatory system works For continuous circulation, the left and the right side of the heart must work together. Here are the series of steps that causes the blood to flow in the heart, lungs and body. The right atria receives deoxygenated blood from two large veins- the superior and inferior venacava. When the atria contracts and the blood passes from the right atrium to the right ventricle through the tricuspid valve. When the ventricle fills, the tricuspid valve closes. Next, the ventricle contracts and pushes blood to the pulmonary artery through the pulmonary valve. The pulmonary artery carries the blood to the lungs where the blood gets oxygenated. This oxygenated blood enters the left atria of the heart through the pulmonary vein. Next, the left atria contracts and the blood flows from left atrium into your left ventricle through the open mitral valve. When the ventricle is full, the mitral valve shuts, Next, the ventricle contracts and oxygenated blood is passed to the aorta through which it is sent to various parts of the body.