Hi Kathryn,

Sorry to hear you're having difficulty, but good to hear from you. I recall you having this symptom prior to this occasion. The diaphragm muscle is situated just below the rib cage and it's actually not to difficult to cause a sprain injury to this area. Under exertion, the diaphragm stretches many times during a single day and helps the lungs expand and contract when you breathe.

The quality of pain subsequent to injuring the diagphragm is described as sharp and acute, rather than dull and continuous. Many people affected find it difficult to take an inspirational or deep breath and consequently, strive to do so in efforts to achieve comfort. This only serves to stretch the muscle further. It's sort of like spraining your ankle and forcing yourself to walk upon it thinking that it will get better under more strain. Additionally, pressure from trapped gas can press against the diaphragm, making even more difficult to breathe. Muscles that are sprained tend to spasm from time to time as well, likely explaining why you feel it "coming on" from time to time.  

In any event, this has nothing to do with your heart and pardon the pun but you can breathe easier. The pain will subside and you'll be fine.

Hope all is well for you and your family.

Best regards and Good Health