Your body thinks Meth is adrenaline in many ways. The chems look a lot alike. You are very much still "on the drug" when you are coming down. I didn't notice a faster heartbeat during this phase, but I don't notice very much, and I don't play with meth anymore ( or too often when I did). Are you sure you are not just more aware of the heartbeat because some of the more acute effects of the drug have subsided? Just a guess. Meth is bad umm-kay. hehehehehehehehe