A normal heartbeat of a adult is 60-100 per minute, with children slightly higher.
If your heartbeat is in the range of 40-50 or even lower, may be you are a long distance runner, or may be its a heart condition that you should consult the doctor about it. However if you think its because your heart is healthier than most people and its not a medical condition, please tell us how much you run per week!
If you heartbeat is in the range of 91-100 or even higher, may be it's time for you to start doing some cardio to strength your heart! Because with the heartbeat rate so high, its just a matter of time before your heart gives out and you will suffer from heart related conditon.