Target heart rate training is one way to determine the best level of intensity for aerobic exercise for you.  To determine your target heart rate you use your resting heart rate, your maximum heart rate and a percentage of the difference between these two numbers to calculate a target number.  Generally the heart rate goes up as the intensity of exercise increases. Training at a target heart rate of 40% to 80% is effective for improving and maintaining your cardiovascular health.

Unfortunately, many people can not use their target heart rate:

Individuals with pacemakers or implanted defibrillators generally should not use target heart rate.  Check with your doctor about how your implanted device affects your heart rate and exercise response.

Many heart conditions including clogged arteries (heart disease), irregular heart beat (arrhythmias), and heart failure affect how your heart responds to exercise.  Also, most people with these conditions are often on medications that alter the heart’s response to exercise.

Medications for high blood pressure, irregular heart beat (arrhythmias), and heart failure slow your heart’s response to exercise. Generally the heart speeds up more slowly and is limited in its maximum rate in response to exercise. Click here for a list of common medications that have an effect on your heart’s response to exercise.
If you do not have any of these conditions and are not on any of the medications listed then you may be able to use your target heart rate as one way to determine your exercise intensity.