I was plugging something in and got mildly shocked from a spark. no symptoms just mild pain in hand. am i ok or will this affect my heart?

Should Be Fine: I can understand your anxiety, but don't fret. You are an otherwise healthy 18 y/o male, without any history of heart issue(s). If you were older, had a past coronary/cardiac history, or had any other untoward result of the "mild shock", i would ask more questions, or send you for evaluation; but, you don't... So, rest easy and watch your fingers : ).

No heart effects: Current has to flow from a source through the central body and therefore the heart for any effect on the heart. You could have gotten a burn on the hand from what happened but if it was a spark, then that is an electron source with very high voltage and almost no amperage, so it will do not damage, just give you a jolt.