M.Lou.B, I salute you for volunteering as a fire fighter.
I'd suggest backing off the high intensity stuff to once or twice a week, as Terry mentioned. But backfill and possibly add some easier rides to build up your base, perhaps 45 minutes to an hour 2-3 times a week where you just get on your bike and go for easy rides: pedal most of the way but don't worry about pushing it. Build up your aerobic base so you'll have that to work off of.
Another thing would be to give it some time. If you've been seriously ill for 10 months, give yourself at least five months (and 8-10 months would be better) to work yourself back into shape.
This test seems kind of arbitrary to me with the 170 peak pulse goal. If none of the above works, keep training for 10-20 years. When your peak heart rate is 165 bpm, keeping your pulse under 170 will be easy.
