Thank you for your query.
You have mentioned that you son has a heart murmur
but you have not provided details about the murmur.
Some children do stop breathing for a short duration when they are startled or undergo pain. This may be a transient phenomenon in most of the cases but it the right thing that you are doing by consulting a neurologist
I hope your son is undergoing regular cardiology follow-up. Small ventricular septal defect
do close with time but larger ones and other defects causing the murmur may require interventions.
I hope I have answered your query to your satisfaction.
Wishing your son all the best.