If you are having early warning signs a few weeks before a heart attack, is it possible to prevent it?

I'm not saying I'm going to have a heart attack, I'm just curious, though. The last time I had my heart thoroughly checked was like 1 1/2 years ago when I was pregnant and having heart palpitations, but it was nothing, just anxiety. Many tests were done and my heart was looked at and I was told it looked perfectly fine. The past month or so (and I have gained about 30 lbs, yikes), I have sometimes been feeling blah and...I guess uncomfortable. I suspect it's from the weight gain. A few times though I have felt a little ache in my chest, sometimes on one side, sometimes on the other. I just started thinking about it and it got me scared that I might have a heart attack or something..I'm 22, I don't want to die because I'm not living a healthy life. So about 3 days ago, I quit smoking cold turkey and have cut out all the sugar and fat from my diet, eating lots of fruits and vegetables and riding my bike 45 minutes per day. I guess what I'm trying to ask is, if those little aches in my chest were early warning signs of a future heart attack, am I working against it by exercising and eating right? I have been more stressed since I've not had a cigarette in the past 3 days, I'm not sure if that increases my risk or not..does anyone know? Once you've had any early warning signs of an impending heart attack, can you prevent it from happening with diet and exercise?