Benzodiazapines are only a short-term treatment.
You're better off addressing your anxieties, deep-breathing, hypnosis, CBT, whatever it takes.
I used to have similar problems and learned after years of trial and error, my heart-rate was a direct result of anxiety.
Thus the recommendation for benzos.
The thing that helped me the most was the realization that my heart was fine.
It was psychosomatic.
If this doesn't help, then cannabis may not be for you.