This happens alot because when you smoke less oxygen is getting into your lungs, causing your heart to beat faster. All you should have to do is relax for a minute, and get some air, you'll be fine. Hope this clears somthing up.



P.S. - However, 170BPM IS a little extreme, and if you've had prior heart problems you had best stop smoking it, or at least get a nice vaporizer.