I have heard plenty of times when an athlete in high school collapses with heart problems and I suggest that if you are worried about this, then you really need to get yourself checked out. Also, if you continue to smoke, well you just may be sealing your fate. Do yourself a favor and while you are able to quit, do it and don't fool around with your health like that anymore.
Your chest/breathing problems are telling you something. Are you listening?
I had chest problems too as a smoker. You should quit, honestly you'll feel much better.
If you're to smoke something, smoke pot, but don't waste your health on tobacco.
Try quitting tobacco and see if you still have a heart problem, it will likely go away even if you do smoke marijuana.
Quitting tobacco isn't that easy, and since you're in school and all your friends are still smokers you likely won't want to quit. If you want to help yourself in anyway at all, at least cut back your smoking to only times when you really really need a cigarette, at first limit yourself to a few a day.
The more cigarettes you smoke, the more Carbon Monoxide you have in your blood stream, and less oxygen is being transported to your bodily tissues.
Your heart is starving of oxygen, and your heart needs oxygen to function when it is playing sports. After you play sports, your heart is strained, and it tries to strengthen itself and this is what is causing you that pain.
I don't think it's good to tell a 16 year old to smoke weed. I hope she can quit it all as weed and tabacoo are equaly bad for your health.