That happens to me alot when I smoke bud, but I still smoke it anyways. I used to smoke it alot when I lived in Austin, and my heart would never beat fast after I had smoked. Now, after I smoke a joint, my heart starts beating fast. I get scared, and I almost freek out because of that. I know damn well that if I freek out because of my rappid heart rate, my high would suck. I allways try to listen to music that is relaxing and soothing when I'm high. That works to some extent.