Need a fitness/exercise expert here...

rytifgates

Ok, well you don't have to be an "expert" if you can help let me know!

Here's my issue:
I am 5'4" and 220 pounds. I am 29 years old.
When I exercise (usually AMT machine 28 minutes) I AM NOT staying in the target heart rate for burning fat like the machine and my research is telling me to. I am up at like 185 beats per minute. The machine says that is almost at the top end of cardio training, not fat loss. What I don't want to do is simply train my body to "go" for a long time. I'm not training, nor do I ever intend to train for any kind of a marathon. Yet, when I try and keep my heart rate at 135 or so, I'm not sweating, breathing heavy or anything. So, I've heard two things. One, that you should stay in your target heart rate for different purposes. And two, that it doesn't matter what your heart rate is, as long as you're exercising, you're burning and will lose weight. What's right? Which should I do? Thanks!!! Oh, and I'm not taking any kind of stimulants or medications that would increase my heart rate. A half hour before I go I usually take a B-12. I don't know if that raises your heart rate or not....