My cousin got extreme heart palpitations when she tried smoking cannabis the first time, which was enough to make her never want to try it again.
Sometimes after I hit a really phat bong with scuff, I go extremely hot and for a little while after my heart rate is really fast compared to normal which if I don't prepare myself for it will knock me back a few steps and I need to just chill out for a min or two.
I would suggest getting high gradually, I think that would stop your heart rate from going threw the roof.