The symptoms of a heart attack
include shortness of breath
, substernal chest pain
possibly radiating to the left arm or jaw, feeling of pressure in the chest, and sweating. Women and diabetics can have much more subtler symptoms, and may not even have pain.
It's rare but not unheard of for a 24 year old to have a heart attack, especially if there is a history of drug use. The fact that it's only when you inhale or exhale tends to point to something non-cardiac in nature. However, it would be a very, very good idea to get checked out by your doctor. You don't want to mess around with your heart. You also might have a severe muscle pull or a respiratory problem that needs medical attention.
Hope this helps!