Hmmm, something tells me I've seen this same post elsewhere.
This might help, it's a web page by an Electrophysiologist. www.drjohnm.org/2011/08/whats-a-normal-heart-rate/
If you have concerns, talk to your family doctor as well.
Heart rate is controlled by a number of factors, very complex, it's hooked up to the sympathetic and parasympathetic nervous systems and responds to hormones and other stimulants.