I Am A 32 Year Med Tech So I Know

I am a 32 year med tech so I know quite a bit my son went to the er 3 weeks ago and his heart rate was in the 40's he is not an athelete so I did cardiac enzymes and thyroid studies on him and they were all normal I find it very hard to believe he has an electrical problem like sick sinus syndrome at the age of 26 and all his labs are normal please I need some advise