Can you have a naturally high heart rate?

I know that people are going to tell me to go to a doctor right away. I have and they said there was nothing seriously wrong with my heart, and that I just have a fast heart rate. Resting heart rate can be between 80-100. According to other health professionals, I shouldn't even be alive during exercise. But when this is going on, I do not feel faint, I do not see starts or keel over the machine, I feel completely normal. It's been this way my whole life. Is is possible to have a high heart rate like mine without it being serious?