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Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium. Left Side. Oxygen-rich blood returns from the lungs to your heart's left atrium through the pulmonary veins.he mitral valve does this between the left atrium and ventricle. The lub is the sound of the tricuspid and mitral valves closing. Each of your heart's ventricles has an outlet valve. The right ventricle uses the pulmonary valve to help move blood into the pulmonary arteries.
After the blood receives oxygen, it returns to the left side of the heart, the left atrium. After collecting in the left atrium, it is pumped into the left ventricle, and from there it is pumped into the aorta, the largest blood vessel in the body. From the aorta, blood courses throughout the body through its arteries. For blood to go in only one direction, forward, it must pass through the heart valves, which function as one-way doors, opening and shutting with each beat of the heart. Just as there are four chambers to the heart, there are four heart valves.