Heart Attack
If you've never experienced this type of chest tightness during exercise before, and especially if you feel increasing pain or discomfort that seems to spread beyond your chest to your shoulders, arms or jaw, you should seek immediate medical assistance -- you may be having a heart attack. Other symptoms include sweating, shortness of breath, faintness and nausea. It's possible to confuse symptoms of a heart attack with those of exercise-induced asthma and many other conditions, so you shouldn't take a chance -- get help immediately.