Thank you for your query on Healthcare Magic.
Your child seems to have abnormality in heart rate
and the rhythm which are known as cardiac arrythmias.
Some arrythmias are paroxysmal means, they come and go.
When there is no arrythmia, the heart rate will be normal and diificult to detect this problem.
This may be the cause for not detecting by the your first Pediatrician
But your child symptoms of palpitations and chest tightness
, even though quite stranege of complaining, still significant.
And in this type of presentation 24 hours EKG monitoring may help to come to a conclusion.
Nothing to worry as the treatment options are available and the specialist will advise you the appropriate treatment.
Hope I have answered your query.