Hi Tara :) So sorry to hear of your problems. They are of course very serious, as you know. You are way to young for this, right? They can fix you up, though. Advances in valve replacement are happening every day!
There are so many ways of calculating your target heart rate. I do believe that this is close to how the folks at the stress test facility may have done it, but I will do a search afterwards to see if I can make sure. I have had 3 stress tests long ago.
First, I think they want you to reach aroung 85% of your maximum heart rate, so:
HRmax = 220 − age
220-27=193 beats per minute (BPM) is your MAX heart rate.
A common way to calculate your target heart rate is:
THR=max heart rate x % intensity
85% Intensity: 193 × 0.85 = 164 bpm is your THR
I believe the docs want people with known, or suspected heart disorders to shoot for 85% of their maximum heart rate. I could be wrong, but I will check.
Of course there are many ways that jocks and other fitness gurus calculate theirs.
Now I will go read your story :)
Sarah, I calculate yours to be 159??? Don't know how they calculated yours... Oh yeah you fibbed about your age, ha ha ha. Just kidding here. You people are just Youngins, lol :)