>I recently added spin class in for cardio. I took my second
>class yesterday morning.
-Spinning is absolutely amazing. I've been doing it for about three months now - about two - three times per week
I brought my own heart rate monitor
>from home. My question is several times I looked down at my
>watch and it was in the 180's!!

Is this safe? I felt
>fine.
-I'm no expert and am just passing along the info I've absorbed from my classes. Most spinning classes are designed to work your heart within a range of heartrates. Depending on the type of class, ie - endurance class will aim to work your heartrate between 70 and 80% of max while interval will take you from 70 - 85% and sometimes a push for a few minutes at the end to 90% - a race day will mostly have you working at 85 - 92% of max heart rate.
I find that my calorie burn is definately higher when my heartrate is sustained for longer in the 80 - 85% range, but at this range you are mostly burning glucose - carbs. When you maintain your heartrate between 65 - 80% you burn more fat - total calories will be less but the fat calories will be higher.
I to was working the higher end when I took my first classes - my endurance was fine - it seemed like unless I hit around 92% of max heartrate that would be when I would huf and puf. Talk to your instructors after class - they should be willing to give you time. The instructors where I go, said that they don't want me to constantly work this high range - it's counterproductive. The want me to focus on getting my heart healthy and strong. Also, it is important to know that it is not how quickly you get your heart rate up, but how quickly it drops when you are recovering that counts. For example when you stand, your heart rate goes up, if you keep your tension and your cadence the same, and sit, your heart rate should start dropping pretty quickly.
If you go to polar.com (the website for the polar heartrate monitors) search around, they have some useful calculators that help you determine what your max heartrate should be and also what your range is at 60% etc. Also, search this forum, there has been alot of useful links about heartrates and calculating them.
Hope this has helped you somewhat. Keep on spinning!!!!!!