( It ( ( ( ( ( returns ( to ( the heart ) ) ) ( through veins ) ) and ) ( enters ( the ( right atrium ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VP (VBZ returns) (PP (TO to) (NP (DT the) (NN heart))) (PP (IN through) (NP (NNS veins)))) (CC and) (VP (VBZ enters) (NP (DT the) (JJ right) (NN atrium)))) (. .)))
It returns to the heart through veins and enters the right atrium.
(ROOT (S (NP (NP (DT The) (JJ right) (NN atrium)) (PP (IN of) (NP (DT the) (NN heart)))) (VP (VBZ receives) (SBAR (S (NP (DT the) (NN blood)) (VP (VBZ is) (VP (VBN pumped) (PP (IN from) (NP (NP (NNS veins)) (PP (IN of) (NP (DT the) (JJ systemic) (NN circuit)))))))))) (. .)))