( They ( ( go ( untreated ( until ( they ( 're ( felled ( by ( ( ( a ( stress-induced ( heart attack ) ) ) or ) stroke ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP go) (ADJP (JJ untreated) (SBAR (IN until) (S (NP (PRP they)) (VP (VBP 're) (VP (VBN felled) (PP (IN by) (NP (NP (DT a) (JJ stress-induced) (NN heart) (NN attack)) (CC or) (NP (NN stroke)))))))))) (. .)))
They go untreated until they're felled by a stress-induced heart attack or stroke.
(ROOT (S (NP (DT A) (NN heart) (NN attack) (CC or) (NN stroke)) (VP (VBZ is) (ADVP (RB often)) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (JJ untreated) (NNS atherosclerosis))))) (. .)))