Hi, why does my heart race for 3 seconds then reset itself?

U could be having: Anxiety symptoms or abnormal heart rhythm, see u physician for evaluation and treatment.

Electrical issue: There is a normal bit of tissue in the heart that is responsible for making it beat, kind of an electrical switch. It has a resting set point of about 72 beats per minute. Sometimes, a few other cells take over, but their set point is 100 beats per minute or more. This can be aggravated with excessive caffeine or stimulant use. It can be dangerous, so see doc if other symptoms with it.