Does the pain ever radiate, especially to your left side, down your arm, into your jaw? Those are classic signs of a heart attack. If it's a quick stabbing pain, it could be angina, and that could be caused by stress. If it is a throbbing pain all across your chest, you could have just stepped off a treadmill after throwing down in a jogging session that would make any CF'er proud, and any normal person wonder what the heck you're so happy about...