I would suggest trying to find a trainer and or physical therapist with specific experience in cardiac rehab. A good physical therapy group or center should have a specialty in cardia rehab as it presents with its own issues. Recovering from a heart attack is hard enough and then adding a rate limiter drug slows you down a bit more. You also have to plug in the orthopedic muscular side to the equation as you are also building back that side. And then there is the question of what kind of condition you were in before your heart attack. One thing for sure you cannot just get aerobic 5 days a week in just a couple of weeks. You need good guidance from a professional. If your MD is not any help for referrals then start networking in your area/friends and or calling P.T./training facilities to see if they have a cardiac program. I asked my wife if as a geriatric PT x 35 years if she had any experience in cardiac rehab and she said no. Every place she worked at had a specific program for cardiac rehab.
Here is an interesting piece written by an MD about his personal experience.
https://www.health.harvard.edu/exercise-and-fitness/do-beta-blockers-interfere-with-exercise