Thank you for your question and I applaud you for keeping a healthy lifestyle. There can be a variety of explanations for the sensation that you experience in your chest and can include heart, gastric, muscle problems to bone and joint inflammation. Hence, I would encourage you to consult your physician for a formal assessment in order to exclude any significant underlying condition.

If you are experiencing intermittent chest tightness and “heart pumping hard”, we will have to assess the details of these events: when these symptoms occur, are they associated with exercise or do they occur saddening as well as their frequency and duration, in order to obtain some clues as to their underlying cause.

From your description, you have undergone quite a few tests for your heart. Hence it will be helpful to review all the results to determine if there are any abnormal findings that may be related to your symptoms. 

The symptoms may be related to a heart condition, irregular rhythm or may even be related to gastric, muscle tension or stress. Hence before we plan for any further tests, I would recommend that you discuss your symptoms fully with your physician to see if there is already a good explanation for your problem.

In your age group, it is less common to have heart disease, although it can still occur. Our heart muscles can be inflamed in a specific condition when viral infection affects our heart function. This however is rare. You may like to clarify with your doctor whether he meant inflammation of your heart muscles, or inflammation of the chest wall muscles which is a benign condition that can occur with exercise, stretching or stress.