Reason For Withdrawing Methadone And Switching To Fentanyl?

yes I have been taking methadone 4 20 years I was on 240mg a day now the past 3 years I,ve been taking8o mg a day.now the va that I go 2 is wanting to withdraw me so i.am taking a fentanal patch 0f a 100 mg so I don,t fell as good an this whole switch thing I don,t why they r c p hanging my methadone 2 a 100 mg, fetanal p they say its got to do with my heart they want me off metadome can u tell me whats really going on?