Well its hard to know without knowing your Max HR. Let's say yours is 194 for the sake of discussion (220-26); then you average 170 / 194 which is 88% max HR. That's a good, hard workout. How do you feel after it? Tired? You should; if 194 is your max anyway.

In my case, I had a Max HR of 203 at 32 years old. So in my case, at 32 yo, (170 / 203) -> 84%, its a good, well paced workout. Now I'm 36 and I don't know my Max HR anymore, I figure it must be somewhere around 195 from the stats I see.

The only way to get your Max HR is to test it, indoors! (so you don't hurt yourself and others) and preferably with a trainer pushing you to go at it more and more and more and more and more (and more, and more, and more) until you almost collapse. Your HR, at that point, is pretty much maxed.

If you are worried about heart conditions for some reason, DO NOT DO THIS ALONE or without medical support.

That said though, until you know your max HR, you cannot infer anything out of a few sessions, you'll need to see how it evolves over time and gauge how you feel.

By the way, the biggest thing I saw wasn't how fast my heart rate kept going; if I exercise hard, it goes high, my body needs oxygen! The important thing is, how long does it take to recuperate? When at 170, how long does it take to go down to 90? The more in shape you are, the faster you'll drop from high to low HR, and likewise, your HR will soar much quicker.

And for the record, young athletes may have died with undiagnosed heart issues but in general, if you DO NOT KNOW about a special condition (family, or past) then, statistically, you'll have a better life expectancy when exercising than if you do nothing because you are afraid of a potential possibility of something bad maybe happening. So if you do not know, ride.