I had a heart attack while riding when I was 46 YO. However it was a minor heart attack and they didn't even fix the artery as it's a little one and would take open heart surgery to get at it. So that is a big difference right there. Then again, a minor heart attack is like being a little pregnant.
I started my recovery by walking also. After about a month I moved on to stationary bikes. About 3 months after the event, I got permission to start riding again. I use a heart rate monitor set to start beeping at 150 BPM to warn me to slow down. I have felt chest pain a few times when I've gotten my heart rate up around 170 BPM.
I've done about a hundred centuries since then and even a few double centuries. I can't go fast anymore but I can go far. I also walk 2 or 3 half marathons a year with my wife. We like to finish at around 3:30 hrs.
Problems: My first cardiologist was pretty clueless about exercise. When I asked what I could get my max heart rate up to, he said 105 BPM. What? And he meant it. He put me on a dosage of beta blockers that would seldom allow me to get my heart rate above 110 bpm. It was horrible for riding. When I suggested doing a stress test to find out when I'd start having problems, he said that I would fail a stress test. I said it wasn't a matter of if, but when, that I was interested in. I didn't get a stress test until 10 years after my heart attack.
Beta blockers, as I mentioned before, are prescribed to keep your heart rate lower. This is from resting heart rate to max heart rate. So they can really slow you down; might make you dizzy when doing things like standing up after sitting for a while; and can cause problems exercising on hot days. Think of your heart being like the water pump on your car. If the pump is working slower, it can't move cooling fluids as well. (I skip a dosage if I'm going to be riding in the heat). Oh! Beta blockers are also used as an anti-anxiety medication. Pretty nice as it also helps you not worry about your heart attack so much. However I noticed that I lost an 'edge' at work. I didn't worry about stuff so much including things that I SHOULD have been worried about.
Finally I got a different cardiologist and she was a marathon runner. We understood each other. Over the course of a couple of years she reduced my beta blocker dosage to a fourth of what it was. I had to promise to wear a heart rate monitor while exercising and keep an eye on blood pressure. We had to bump up a couple of BP meds instead. I didn't have high blood pressure before the heart attack so something changed once I did.
Speaking of BP meds, besides beta blockers I did have a major problem with a diuretic medication. The diuretic worked like a champ in reducing my BP by 10 points overnight. I had to pee a lot more as that's how diuretics works. However I started having gout attacks left and right after not having one for years. I'd successfully controlled my gout problem through diet modifications. However getting dehydrated is one way to bring on a gout attack. So I had to go off of the diuretic. If you are on a diuretic and that big toe (or some other joint) starts hurting, talk to you doctor.
Good luck. Take it slow and build back up. I bet they have to rein you back as you sound like you are chomping on the bit. As my cardiologist has said more than once "I wish all my patients were like you." Hopefully you doctor will be saying the same to you.