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.
Did he have surgery on his heart after the heart attack?