Aerobic exercising while on metoprolol

Perfectly understandable to wonder how to do this, and how to overcome your reticence to working harder to gain ground on your fitness.

Gaining fitness is a slow process. It needs time for your body to adapt to the new levels of stress. At 78, it could take almost twice as long as it might have taken only 20 years ago., but certainly when you were only 30. Gaining fitness usually requires additional muscle mass in order to operate with greater ease and less strain, and your heart and diet have to afford your body the way to do that. It might not be much muscle mass, but you'll undoubtedly need more, especially if you know you have 'let yourself go' some in recent years. Again, this takes time. So, my advice is to use your common sense, your gut feel, and what motivation you can muster, to begin the journey, literally one step at a time. As you do more, you should...SHOULD...naturally increase capacity in speed, strength, and also in heart function. However, there's the metoprolol. Everyone reacts slightly differently to that drug. For me, I feel it slowed me down. I have been a competitive runner my whole adult life, but metoprolol made a change in my output, and I slowed noticeably when taking it. This is probably what you feel as well. My cardiologist denied it, but I have nothing else to pin my diminished capacity on, so that's what my assumption is.
Still, my advice stands; do what you know you can, and no more. Next day, or two days later, do the same, maybe add another 'round-the-block' or whatever...a bit more. In time, you should see yourself going increased distances, but also at a somewhat faster pace. It's a natural process. Some days, you may want to try picking up the pace. Go until you find yourself puffing too much, or until you'd had your fill of it. I would not pay too much attention to heart rate because you are only going to be walking, maybe cycling (??), and not running or stair climbing for 30 minutes at a time. I mean, there's nothing wrong with satisfying yourself that your heart hasn't run up to 150 BPM, but my heart routinely runs up to about 145 BPM and I'm soon to turn 73. And this IS on steps, many of them, going up a rise that takes me about seven minutes in total, over 330 steps, plus some steep path. One last time, start out doing what you can do, add a small bit every other or third time, take rests and rest days if needed, and keep at it. Shouldn't be more than two or three months before you notice a substantial difference...hopefully.
Note that this presupposes you are actually and essentially healthy and have no other warnings or cautions about physical activity from doctors.

I fully agree with you that building aerobic endurance slowly using common sense is the best way to go. I have been working on my endurance problem for over two months and have developed some questions about aerobic training with underlying heart issues and looking for advice (or lack of) from my doctors.

First, I guess I really don't understand what is involved in aerobic training. I assumed that the object of aerobic training was to work the heart at near or near the maximum heart rate stated for my age. I had done this about 20 years ago with reasonable success. Now I am on a heart rate limiting drug (metoprolol) and I have not been given any guidance regarding my current maximum heart rate limit which seems to be on the order 110 bpm. What are reasonable limits for a person in my condition?

Second, I am not convinced that my short windedness is directly related to my aerobic fitness. My experience with my aerobic workouts that my heart rate initially drops and slowly recovers when I increase my workload is counter intuitive and explains why I experience a sense of fatigue and shortness of breath during my work outs. And it explains why I experience a temporary shortness of breath when I climb stairs or begin walking up hills.

I am fully committed to maintaining a healthy and active life after my heart attack which includes aerobic activities; I just want to make sure that I do it in a safe and sane manor. I know I am not the only one with these heart rate issues, and I am looking for answers regarding my heart rate limits and best practices for recovery.

All sensible wonderings. Have you been checked out by a pulmonologist? Maybe something about your oxygen exchange apparatus needs some attention. What is your ejection fraction? How is your ferritin? Heme iron? Magnesium determined by a CRP? All these things could point to a defect in some aspect of your routine maintenance.

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