Cramping, sort if jittery type pain always inside chest on left side and under breast bone an shortness of breath. Ekg was fine what could it be?

Heart or not? An ekg only shows the heart's rhythm during the 10 seconds that it was performed. A 30 day heart monitor can catch the heart rhythm during symptoms to see if an abnormal rhythm is occurring. And many other conditions can cause chest symptoms, including muscle spasms and other non-heart diagnoses. Take note of when you feel symptoms, such as with exercise or with breathing, and talk to your doctor.