It is recommended that your maximum heart during exercise be no more than the number 220-your age.
Your goal is to exercise at a percentage of this max rate. of your MHR. To burn fat and not blood sugar for energy, you want to stay in the 50%-70% of your MHR. So if you are 40, your max heart rate should be 180. So, if you train at 50% of your MHR that means your pulse will be at 90 BPM (Beats Per Minute) or .5 X 180. 60% is 108 BPM, 70% is 126 BPM. If you go higher than 70% you are burning blood sugar for energy, not fat.
You dont want to go above your max heart rate, it could lead to heart issues and death.
It sounds like you are in OK shape, remember aerobic activity causing your HR to go that high means you are out of shape and not conditioned. Patients who are de-conditioned will quickly reach high HR's. WIth moderate to strenuous exercise, you really dont want your heart to race to 200 since it puts you at risk for a heart attack. You want to exercise with your pulse at about 80-110 (closer to 90-110) for optimum cardiovascular conditioning as well as fat burning.