blood carries the oxygen you were inhailing and the oxygen rich blood will go to the lungs andĀ lungs give it to the heart and heart give it to the 3 blood vessels ,heart will pump the oxygen rich blood to its self(so heart will function) , and throughout the body(and body gets the oxygen from the blood) then the heart will get the oxygenated blood(wich is the blood that the body was taken the oxygen) and give it to the lungs so the lungs change it to oxygen rich blood and the heart do again the same . every heart beats the cycle happens :)
but remember all systems work together, not just lungs and heart :)

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