Because the heart pumps the blood through the lungs, the heart must function properly for the lungs to function properly.
(the heart; pumps; the blood; through the lungs) (the heart; must function properly; for the lungs to function properly) (the lungs; to function properly; )
the heart the heart the lungs
pumps must function properly to function properly
the blood through the lungs
for the lungs to function properly