Lyn- unless you are told by your dr. that you can't tolerate a higher heart rate, don't worry about it. I always use a higher heart rate to help increase my fitness and endurance. I will see a higher rate on hills especially. The way it works is that say you are doing some intervals and you add some sprinting or a hill that increases your heart rate, do it as long as you can tolerate it, then walk it down to 75% of max, rinse and repeat for about 20 min. If you do something like that 1-2x/week, within a couple of weeks your ability will improve, you will adapt. Its like a weight workout for your heart, you ask your muscles to work heard, not just light weights/high reps, in order to build strength. I hope that makes sense.