Everybody knows that a good resting heart rate is highly indicative of an overall healthy individual. A healthy heart means your body is being supplied with the appropriate amounts of blood, oxygen, and nutrients for whatever you are doing at that time. So when your anxiety is high or fight or flight response kicks, your heart rate picks up to increase the amount of blood flow to your muscles and throughout your body so that you can react quickly if needed. And if you are a runner, a good heart rate means your body is efficiently distributing blood and oxygen to your muscles and organs to keep you moving and help you increase speed, conquer those hills, and achieve your goals.
For average adults, the standard target heart range for healthy individuals is between 60 and 100 beats per minute. However, many runners, athletes, or people in excellent cardiovascular condition may have a lower heart rate between 40 and 60. This is not abnormal, nor should it alert you to problems. It simply means your heart is extremely efficient!
However, if you are below 60 beats per minute and not an athlete (or if you are a conditioned athlete and have a resting heart rate of below 40 beats per minute) then consult your doctor - especially if you experience dizziness, fatigue, or general malaise. A low heart rate may also alert you to malnourishment, as many people who are not getting in adequate nutrients and macronutrients for their activity levels can experience a dangerously low heart rate. And if your heart rate is above 100 beats per minute, you may be suffering from tachycardia, a condition defined by an abnormally fast heart rate. Not only may you feel dizzy or faint from tachycardia, but you could experience a tightening of the chest and sensations that make you feel like you are having a heart attack.
One final word on heart rate has to do with abnormal heart rhythms, which can be dangerous especially for runners. Not only the beats per minute but the rhythm/pattern of heart rate should be steady and regular. This might be indicative of a more serious heart problem.