I take klonopin and before i started the regimen i did some thorough research into side effects and other possible problems. I don't believe a rapid heartbeat is one of the recognized typical side effects. Since Klonopin is a benzodiazepine, it is used for a myriad of diagnoses; seizure, muscle spasms and convulsions, which seem to be counter-effective to the side effects your experiencing. My advice to you would be to contact your doc. They may need to reevaluate your dosage or sensitivity to the medication.
Also keep in mind especially if you're a new user of the product, that a lot of anxiety and stress can come from the fear of having a rapid heartbeat from the medication. meaning, if you're worrying about it, it may be more likely to occur. Your doc prescribed these meds to help you and sometimes the transition can be a little rocky. Call your doctor and let us know how everything turns out. Good for you for keeping a sharp lookout on your health and well-being, instead of ignoring what your body is telling you.