Well, I'm 58 years old now, and I guess the rule of thumb about heart rate is the old 220 minus your age thing, which for me would be 162. I regularly see numbers way higher than that on my hrm when I'm climbing, and I asked my doctor about that. He said that as long as the number dropped back down to 120 or so within a minute or so of resting I was OK. But if it ever went way up and stayed up, I should dial 911.

Typically, when riding along at my usual (slow) pace on the flats, my hrm reads 125 to 135.