Hello. Thank you for your question and welcome to HCM. I understand your concern. It is good news that this is a regular heartbeat and a sinus tachycardia. High body temperatures, and fever in general, is a state where the organism goes through a lot of changes. Temperature acts on its center in hypothalamus (a specific region in the brain) and provokes a series of changes, one of which is sinus tachycardia. When the fever is cured and body state comes to normal, so does the high heart rate. However, if your suspicion is that he was bit by a tick, I recommend you to consult an infectious diseases specialist, to carefully determine what micro-organism is causative of this situation. I hope I was helpful. Take care. Good day, Dr. Meriton