I Am 76 6-1 207 Feel Good Generally But Run

I am 76 6-1 207 feel good generally but run short of breath when walking Do well pushing a grocery basket or hanging on to sides of treadmill. Have 5 stents in my heart 1 rt knee replaced and 5 back ps Also bp of 145/65 taking too many meds My pc and cardiac DRs say my heart is good no a fib and lung show clear why do I have such a hard time walking? Don Holtrop