My response is pretty much the same as everyone else's....1. see doc. Immediately. 2. maybe you need some pulmonary function tests...may have some exercise induced asthma going on. 3. Are you adequately hydrated? Sometimes if you are even a tad dehydrated it will affect your tolerance. 4. DO you have any other medical issues such as diabetes, high blood pressure, etc that may be influencing your tolerance?

I think that you absolutely need to find out if you indeed had a heart attack all those years ago, that should be first and foremost! Let us know what's going on, ok?