My Husband Is A Heart Patient, Taking Statins, Good Blood

My husband is a heart patient, taking statins, good blood work, had open heart surgery 18 yrs ago, and has had three stints. he has a pulmologist who gives him steroid shots for bronchial congestion from time to time. really helps. However, in the last few months, he had noticed his legs getting weaker, and he's very short of breath when he walks anywhere other than in the house. Any clues? heart? Don't know which to go to. Heart, Pulmonologist, internets? Thank You