I think the Garmin's or any other heart rate machine's false readings are when there is interference, and the cyclist is not going up a killer of a grade. My hunch is the heart rate of 220 was probably accurate, given the circumstances.

Mr. Silver, good for you for getting as far as you did. I am envious. Honest to goodness, I wish I could read a post like this and say, "Huh, I go up 10 miles of 28% grades every day and my heart rate doesn't go past 150." In my dreams, only.

Like Lisa said, stop. Whenever you feel something going wrong, stop.

But gosh, that is brave, to even try a grade that steep. Kudos.

Darcy