( ( The valves ) ( ( ( ( ( ( control ( ( the flow ) ( of blood ) ) ) ( ( ( through and ) from ) ( the heart ) ) ) and ) also ) ( ( prevent ( backflow ( of blood ) ) ) ( by ( their leaflets ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS valves)) (VP (VP (VBP control) (NP (NP (DT the) (NN flow)) (PP (IN of) (NP (NN blood)))) (PP (IN through) (CC and) (IN from) (NP (DT the) (NN heart)))) (CC and) (ADVP (RB also)) (VP (VB prevent) (NP (NP (NN backflow)) (PP (IN of) (NP (NN blood)))) (PP (IN by) (NP (PRP$ their) (NNS leaflets))))) (. .)))
The valves control the flow of blood through and from the heart and also prevent backflow of blood by their leaflets.
(ROOT (S (NP (NNP Heart) (NNS valves)) (VP (VBP prevent) (NP (NP (DT the) (NN backflow)) (PP (IN of) (NP (NN blood)))) (PP (IN from) (S (VP (VBG happening) (PP (IN in) (NP (DT the) (NN heart))))))) (. .)))