Hello, and thanks for your medical question on eHealthForum.
Based on the history, additional information is needed regarding the cause of the heart murmur. The presence of heart racing, difficulty breathing and chest discomfort could be due to many conditions related to the lung or the heart.
Though heart burn can cause chest discomfort other important causes like childhood asthma, etc has to be ruled out. You may consider to consult a pediatrician who can examine your son and do relevant tests like a Chest X-ray and an Echo cardiogram to diagnose the current condition and initiate necessary treatment.
I hope this helps.