My son's heart......?

Ok Well ever since my son was born the pediatrician always said That the had a real fast heart beat. Dr. Patel never seemed alarmed about so that was that...My son is 6 and yesterday he asked if my heart hurt? I told him no and he started to get like a lump in his throat and said that his heart was hurting! i got worried and told him Just to relax. Then after an hour later he said he felt better. Today he woke up fine for school. Im still worried though why would a 6 year old say his chest hurt if he never has said that before? Should I take him to the Doctors or is nothing??