( ( Cardiac muscle ) ( ( forms ( ( the mass ) ( of ( the heart ) ) ) ) . ) )
(ROOT (S (NP (NNP Cardiac) (NN muscle)) (VP (VBZ forms) (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (DT the) (NN heart))))) (. .)))
Cardiac muscle forms the mass of the heart.
(ROOT (S (NP (NNP Cardiac) (NN muscle)) (VP (VBZ makes) (PRT (RP up)) (NP (NP (JJS most)) (PP (IN of) (NP (DT the) (NN heart))))) (. .)))