Sorry to hear of your problems with those drugs. To begin increasing your distance and to improve your overall health you will need to move a bit farther each day. After my quad, July 24, 2015, I could barely stand up without fear of falling down. I used a shopping cart as a "walker" the day I left he hospital and slowly walked around the grocery store to get the items I needed immediately. Finally after a full year had passed I managed the long walk of the local Heart Walk and walked a 5K. Took me longer than everyone else, but managed it.
Have you gone to Cardiac Rehab? If not, please do so. They give you a program that will increase your endurance and monitor your progress and report it to your doctor. I too had been on those drugs, stayed on Coreg for over 3 years cuz it kept the migraines at bay and finally tapered off and no more migraines.
Your heart probably needs some supplements to strengthen it. CoQ10, Vitamin B complex, Carnitine, DRibose (yeah it's a sugar, but it is what a damaged heart needs), Hawthorne extract are all recommended for hearts. Look them up, don't just take my word for it.