I just had a major heart attack and I am really scared about the reco?

I dunno 'bout you, but I have had some kind grownups kick my arse a coupla times in my adult life. It was richly deserved, looking back, and served to make me more conscientious and responsible. For what I do...or fail to do. You say you have two sets of grandparents who had genetic problems with their hearts. One could hardly blame you if you have that disposition yourself. From there, anything you opt to do out of dire and strident motivation is probably going to serve you well. Are you now motivated?

Get good sleep.
Eat food you have to clean, strip, peal, and cook for yourself. Avoid things in cans, boxes, tear open bags, ready-to-eat. They all contain additives of a kind that make you think about having more of it. It's marketing and it is the undoing of many a sound heart.
Move your body. Twice, three times each day, move at a brisk walk for at least 15 minutes, or once a day for 30 minutes.
Avoid alcohol and recreational drugs. The former is a suppressant of the central nervous system, not to mention what it does to your liver, and the latter is just flirting with one-pop-away-from-the-biggest-mistake-you'll-ever-make.
Sometimes it helps to get better friends. Some may smirk at this advice, but think about it. Are you consorting with people who are interested in your good health?
Watch how you spend money. If you're a spend-thrift, and live paycheck to paycheck, it's a stressful life. Any kind of stress, including the kind you're not aware of, puts a strain on the body by raising both cortisol and adrenalin. Those two are great when you have to fight for your life, but not great when you're drinking beer with buddies or surfing the internet, arguing with strangers on chats.

I hope you'll get other considered advice.

I had a stroke, not a heart attack, but I understand the fear.

It will probably stay with you for quite a while. (For stroke patients, fear of another one can be paralytic.)

The important thing is not to let fear overtake your entire life. That's not as easy as it sounds, I know, but try to think of it like driving a car -- you know that many people are injured in car crashes every day, but you don't let that stop you from going places.

I have an episode about fear on my YouTube channel:

https://www.sturdyhealth.org/advice/life-changes-after-a-heart-attack/

I feel for you, any issue with your heart is anxiety-producing. If you have a cardiac rehabilitation program in your area, I would highly recommend taking part in it. They can help you get back on your feet and help you determine what you can and can't do.
Also, if you can find a support group, please do so - a group that can help and support you through any lifestyle changes you need to make.
All the best to you!

I have read many times, that genetic factors are a small percent of problem. I believe that eating and lifestyle habits are learned and copied from parents, grandparents etc. etc. Take a good look at your weight, are you overweight?

Do you consume anything with caffeine? Colas, coffee, chocolate, Mountain Dew which has more than cola, energy drinks. Do you eat processed meats, or much meat Do you munch on processed foods, chips, cookies etc. Do you drink sugary drinks, lots of juice, diet drinks? Do you eat bread etc containing refined flour? Cakes etc. Straighten up your diet and stop watching the boob tube and get out and walk.

I am 77n yrs old and take no meds but had afib in the past. I walk up steep hills every day. I work at maintaining my weight which is at present 123 lbs. I prefer 121 and will get there.