Heartrate is great for building and maintaining a certain base level. This is essential for any one that wants to do some serious racing. I use a Garmin FR60. This is a great piece of equipment, and I got mine with the speed sensor for around $150 off amazon. One of the best features is that it comes with a little wireless usb adapter that you plug into your comp it then every time you walk near you computer with a new workout on your watch it uploads straight to garmin.com. It gives detailed reports on heartrate, speed, and cadence(I know most mtn bikers don’t use it, but I like it). The only issue I have with it is for some reason Garmin thought it would be a good idea to base calories on speed if you are using the sensor and this is a big no no(works fine for road bikes but not for mtn bikes), but I am hoping they correct this in one of thier updates.