I have Supraventricular tachycardia so mine sometimes jumps to 260-265
Why do some people have fast heart beats?
It's mainly caused by the three types of Tachycardia. This site has a great explanation for causes of this.
Tachycardia | Fast Heart Rate - American Heart Association
www.heart.org/.../Tachycardia-Fast-Heart-Ra.
Could be their diets. Could be their genetics or DNA. Or they could be like me, where they used to drink a lot of energy drinks a few years back and regret doing it.