Hi,
How are you? It is good that the ECG and stress test were fine. Chest pains can be due to cardiac and non-cardiac causes such as pulmonary, musculoskeletal and gastrointestinal in origin. If the pain occurs after work out, this could be related to musculoskeletal causes such as muscle strain. Rest and muscle relaxants may help. Also, drink plenty of fluids and eat high-fiber diet to help with your constipation. Take care and do keep us posted.
If you lay on your left side, and sleep that way most of the time, it could be caused by that. Try switching sides when you sleep. Sometimes that is all it takes for the pain to subside. It may take several nights before you notice any relief, but it's worth a try.
As far as constipation goes. Get some stool softeners and try them. They can be purchased OTC, and do not cause undo abdominal pain.
I've been throug a major GI bleed, heart attack, CHF, and I am in end stage renal, and none of it has ever been caused by constipation. However, "if" you have a heart problem, the last thing they want you to do is strain when you go to the bathroom, so they prescribe stool softeners. So I suppose they must be safe.
Of course in this day and age they have a pill for EVERYTHING, and they aren't happy until you're on several of them, so that is also something to keep in mind.
Good luck....