Can you make your weak heart strong?

Yes .Without doubt you can increase the strenght of Heart. With GODs grace and consisistent efforts , I have achived far better heart health in 2 yeras after severe heart attack when i was 57 . Now 59 . Here are steps.
1.Meditation for 20 minutes , 2 times a day to instill positive state of mind.
2.Exercise for 15 minutes before Bearkfast in Must. You can take a brisk wlak also.Ensure Herat rate is targetted and achievd as per your cardiologist advice. You can slowly increase from 10 minutes to 30 minutes with2 minutes increase very week.
3.Ensure medicines are taken in time. Take a second opinion about cholesterol lowering medicines.I stopped it about 1 year back. I do not have much faith in statins.MY LDL and Lipid profile is good.
4.DIET plays very very critical role.Go for fish and balance veg diet.NO fast food and meat.Redice Sugar and Salt by 60 % in 2 minths.
5.Good simple formula -5F , 10 M , 8S , 16 M , 32 P
5F -5 Fruit servings in a day,10 M -10 minutes of Intense Exercise before breakfast,8S -8hrs of good sleep and rest , 16 M -16 minutes of Meditation , 32 P -total 32 minures of Physiothrapy, Pranayam (India breathing system ), Patanjaili YOGA and other light /relaxing exercises
MUST Change sedentary habits and keep moving -NO Strenous games.
6.Massgae done regularly (say 2/3 times a week 0 is Excellent.It detoxifies and helps keep muscles in good condition.You can do self massage by any good oil , say Red Oil avalabilae in Indian stores and
take hot water bath after 30/40 minutes of massage.
7.Prayers and Mantras help Greatly.Try for simple life style and help heart patients.
There are many other things which i do in India. You may like to join me on fb-kishan vasekar (group happy heart )
I survived 40 days stay in ER .SPEAKING FROM EXPERIENCE

Talk to your cardiologist. There is such a thing as cardiac rehab, I don't know if you'd be a candidate tho.