breathing; stamina difficulty

was a smoker for 30 years. had a heart attack at age 53 and needed immediate heart surgery --- a CABG
quadruple bypass. it's been approximately 6 years and have stopped smoking cigarettes for the past 7 months
and STILL, am unable to briskly walk as i did before (i loved to walk) or walk moderately, for more than a couple of
blocks without feeling WINDED and have to stop and get my breath back.have had  lung function tests without good
results, meaning my score's down. have the beginning stages of COPD. is there anything i can do or medicine i can
take that will hopefully improve this insidious condition??!!!