It's taken me a year to go from barely being able to do anything (100 bpm) to being able to do 130-135 bpm for 45 mins (about 75% of age predicted max heart rate) without too much ill effect. 20 mins at 145 bpm will still mess me up for a couple of days. I've been back at work, so that's slowed my progress lately... (partly due to time constraints, partly because there's times where I can't risk being messed up for a day or two if I were to push myself too hard).

Zoloft has been great for me (75 mg). But of course, everyone's different. I had minimal side effects going from 0-50mg. When I went from 50-75mg, I felt a little too chill and a bit sedated for a couple of weeks, but that subsided. The biggest benefit is that it's made me less stressed out about my symptoms.