I just turned 42, and both of my pregnancies were also high risk, because I've been a Type 1 diabetic since I was 13 (1979). I turned 25 while I was pregnant with my oldest, Jeremy, and I turned 39 while I was pregnant with my "little guy" Noah, who is 2 1/2. My boys are 14 years and 9 days apart! :)
I guess the first piece of advice I have to offer you is, if you weren't already doing a form of exercise *before* you got pregnant, now is NOT the time to start it! :) I'm sure your doctor will advise you that the best form of exercise you can do during this pregnancy is simply to walk, and make sure you don't "overdo" anything.
I have a form of heart condition called tachycardia (really fast heart beat) combined with a normally low blood pressure. (tachy from my mom, low BP from my dad ~ really "freaks" a lot of nurses at the dr's offices! LOL) The tachycardia got really aggravated with my 2nd pregnancy, as did my asthma. The biggest problem I had at the beginning of my pregnancy with Noah was the extreme vomiting I had going on. I got pregnant in late August, and by the beginning of November, I had to be put in the hospital for it, because it wasn't stopping. :* In the end, I'm really glad that happened, because I ended up with some GREAT doctors in the process! New endocrinologist who actually got me started with my insulin pump (no more daily+ shots, YAYYY!), an AWESOME OB/Gyn, and a fantastic cardiologist, too! :D
Since you are high risk, your OB should have you come in more often than a "normal" OB patient (at least both of mine did), and you may also get to have more sonograms!! (that's really cool ~ I used them to see my babies' faces, and that helped me with choosing their names; I know...that's "cheating", but it was fun, anyway!)
You can call me anytime. My # is ###-###-####, and I'm a SAHM to Noah (Jeremy is usually with his grandparents, or his aunt and uncle's because his cousin Travis is the same age). I'm so excited for you!! Maybe we can get together sometime and visit.