( ( ( Your ( heart valves ) ) ( -LRB- ( ( ( bicuspid and ) tricuspid ) -RRB- ) ) ) ( ( ( are essentially ) ( ( check valves ) ( that ( ( ( prevent ( backflow ( to ( ( the atria ) ( from ( the ventricles ) ) ) ) ) ) , ) ( forcing ( the ( ( fluid ( -LRB- ( ( that ( 's blood ) ) -RRB- ) ) ) ( to circulate ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (PRP$ Your) (NN heart) (NNS valves)) (PRN (-LRB- -LRB-) (VP (VBN bicuspid) (CC and) (VBN tricuspid)) (-RRB- -RRB-))) (VP (VBP are) (ADVP (RB essentially)) (NP (NP (NN check) (NNS valves)) (SBAR (WHNP (WDT that)) (S (VP (VBP prevent) (ADJP (JJ backflow) (PP (TO to) (NP (NP (DT the) (NN atria)) (PP (IN from) (NP (DT the) (NNS ventricles)))))) (, ,) (S (VP (VBG forcing) (NP (DT the) (NN fluid) (PRN (-LRB- -LRB-) (SBAR (WHNP (WDT that)) (S (VP (VBZ 's) (NP (NN blood))))) (-RRB- -RRB-)) (S (VP (TO to) (VP (VB circulate)))))))))))) (. .)))
Your heart valves (bicuspid and tricuspid) are essentially check valves that prevent backflow to the atria from the ventricles, forcing the fluid (that's blood) to circulate.
(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))))))) (. .)))