Sorry to hear about your past heart attack. It can be very difficult to tell the difference between heartburn and heart attack when your symptoms really mimic those of heartburn.
You did the right thing taking the aspirin when you experienced the discomfort that was similar to your heart attack, however, any discomfort that is similar to previous heart attack symptoms or "scares" you should be evaluated immediately. You didn't go to the emergency room, but you should call your cardiologist and explain the episode. He/She will most likely want to re-evaluate you with another stress test or even a cardiac catheterization.
Heart attack symptoms can really vary. The classic symptoms are chest,left arm, or jaw discomfort, shortness of breath, nausea, and sweating. Not everyone gets the classic symptoms...heartburn type discomfort, shoulder blade pain, extreme fatigue, decreased energy levels can also indicate a problem.
It is very important to keep all of your risk factors well controlled. These include blood pressure, cholesterol levels, sugar levels, don't smoke, exercise regularly (as permitted by your healthcare provider), and eat a healthy diet.
Finally, take all medications as prescribed and see your cardiologist routinely. Definitely make an appointment (if you haven't done so already)to let him/her know about your recent experience. It may only be heartburn, but there is no way to be sure until you check out your heart first.