Deoxygenated blood flows into the right atrium via superior and inferior vena cava, right atrium contracts which pumps the blood into the right ventricle through the tricuspid valve, once it is filled the tricuspid valve closes to prevent backflow, the right ventricle then contracts that causes the pulmonary valve to open, pumping the blood into the pulmonary artery that travels blood into the lungs, closing the pulmonary valve, and relaxing the left atrium which accepts the oxygenated blood.