If your husband had an enlarged heart, that would have shown up on the testing he had done. I would also tell him to see a cardiologist.
It is good that you have discussed with your doctor, chest pains should always be checked.
I assume the blood pressure and heart rates are also normal, as per the stress and EKG tests. You can also check these yourself, even the HR can be done at home with no tools other than a watch.
Is he on any medication? I suggest taking an aspirin a day with a meal if that does not cause problems such as upset stomach. This is an easy, inexpensive, and effective therapy for many heart problems. Was the doctor a primary care or was a cardiologist involved in the diagnostic work already done?
Try not to focus on the symptoms while at the same time being conscious of any changes, something that is hard to do, but important as anxiety can cause false heart symptoms.