Blood from the lungs is carried back to the heart by the

Pulmonary vein

Pulmonary circulation is the movement of blood starting from the heart, where deoxygenated, or carbon dioxide-filled, blood leaves from the right ventricle and through the pulmonary valve, then into the left and right pulmonary arteries and arrives at the lungs. During the process of respiration, the carbon dioxide is released and oxygen is added to the blood. 

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