sourdough

What heart rate should you be aiming for on a 3 hour bike ride?

I was told you should keep it well below 70% for a good workout. And it was not healthy to keep your heart working that high.

I figure if I was not weak our out of breath I was doing ok.

Would a heart rate moniter be helpful or is this taking the fun out of bike riding?

What sould a person pay for a decent heart rate moniter?

Thanks