Atrial fibrillation, on Coumadin.
 Patient has history of stroke
(ROOT (FRAG (NP (JJ Atrial) (NN fibrillation)) (, ,) (PP (IN on) (NP (NNP Coumadin))) (. .)))
(ROOT (S (NP (NN Patient)) (VP (VBZ has) (NP (NP (NN history)) (PP (IN of) (NP (NN stroke)))))))
( ( Atrial fibrillation ) ( , ( ( on Coumadin ) . ) ) )
( Patient ( has ( history ( of stroke ) ) ) )