hi good to know its anxiety not your heart! I mean you're only 21 theres no reason your heart suddently goes wrong... the antidepressant drug should be very effective from my own experience but only after some 2 weeks so you need to keep taking although no result immediately.
Anxiety treatment usually has to go for years to completely restore you to normal state so never stop the medication on your own, ALWAYS SEEK YOUR DOCTORS ADVICE FIRST!
also the heart attack you said, never heard of it.