If my child is fainting, does he have a serious heart condition causing it?

Probably not. Fainting is common in childhood, and usually not from a heart condition. It is best to talk it over with your child's pediatrician. They can give good advice, and perform tests if indicated.
See belwo. Unlikely. But, it depends on when he is fainting. A warning sign for an underlying heart problems in kids is loss of consciousness with sports. Fainting with position changes, in overheated environments, and fearful situations maybe normal. Discuss with your doctor. Also if there is a fh of sudden cardiac death in young healthy people, your child maybe at an increased risk of having a heart proble.
Most benign. Most of these turn out to be poor hydration, an emerging illness, or inconsistent dietary habits. I do check a EKG for evidence of a heart rhythm issue.Depending on the history I sometimes get an EEG.I also look at a basic CBC for evidence of illness or anemia.This happens pretty often in a pediatricians practice. .