It's important to find your personal target heart rate. This will assure you're getting your heart rate up high enough, but not too high. Take your age away from 220 and that is your maximum heart rate level. If you are doing low to moderate-intensity exercise, your heart rate should be at 60 to 75 percent of your max heart rate. If you are doing high intensity exercises, you should be at 80 percent to 90 percent of your maximum heart rate level.