Did he have surgery on his heart after the heart attack?
Hello~It sounds like a form of angina, has he had any echocardiograms done? Also, sometimes, if the heart-beat is irregular, symptoms like this can be experienced, especially with A-fib. I would definitely see another cardiologist if possible and ask for the echo and to wear a king of hearts heart monitor, this will pick up any abnormalities that are going on while he is wearing it.
We have a wonderful heart forum here, I am going to recommend that this post be transferred over to them, they will probably be able to give you some more information as well.