( ( The ( right atrium ) ) ( ( ( pumps ( the blood ) ) ( to ( ( ( the ( right ventricle ) ) , ) ( which ( ( pumps it ) ( to ( the lungs ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ right) (NN atrium)) (VP (VBZ pumps) (NP (DT the) (NN blood)) (PP (TO to) (NP (NP (DT the) (JJ right) (NN ventricle)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBD pumps) (NP (PRP it)) (PP (TO to) (NP (DT the) (NNS lungs))))))))) (. .)))
The right atrium pumps the blood to the  right ventricle, which pumps it to the lungs.
(ROOT (S (NP (NP (NNP Blood)) (PP (IN from) (NP (DT the) (NN body)))) (VP (VBZ enters) (NP (NP (JJ right) (NN atrium)) (PP (IN of) (NP (DT the) (NN heart)))) (SBAR (IN before) (S (NP (PRP it)) (VP (VBZ is) (VP (VBN pumped) (PP (PP (TO to) (NP (DT the) (JJ right) (NN ventricle))) (CC and) (RB then) (PP (TO to) (NP (DT the) (NNS lungs))))))))) (. .)))