what are the best ways to prevent a heart attack?

im a 15 year old female, somewhat overweight, and i get pains in my chest sometimes. i have asthma, so i think thats what its from.

what are the best food to eat, what should i avoid?
what excercises should i do?
like should i do cardio more?

what should i avoid eating, and what excercises are the most effective to prevent haveing a heart attack?