The marvelous mechanism that is your body has many signals to let you know when problems arise. If you're exercising and you encounter chest pains, shortness of breath, or other indications that something is awry inside your rib cage, don't ignore them!
Please, if any of these symptoms arise, stop exercising, consult a doctor, and resume the program only under the guidance of a medical professional. Physicians can wire you up and run a comprehensive set of diagnostics to find out whether something is seriously wrong or you're just trying to push your body beyond its natural limits.
Ignoring these signals from your body is the height of folly. It can lead to all kinds of tedious and exasperating side effects such as sudden death.