A sour taste or bitter fluid in the back of the throat are classic signs of heartburn. Ditto if the problems increase at night or while bending over.
On the other hand, shortness of breath, lightheadedness, fainting, sweating or pain radiating down the arms or up to the shoulders are clear warnings of a heart attack. Other signals for both include nausea and vomiting.
So here's the bottom line: If in doubt, see a doctor -- immediately.