You can do cardio while using propranolol, but I'd recommend that you only use 10mg, or even 5mg. At these doses, your heart beats smoothly, with low intensity. No clunking heart beats, no palpitations, no tachycardia. Just smooth heart beating. It will lower your blood pressure a little bit.
The better thing to do would be to do your fasted cardio without propranolol, because with less adrenaline action after taking propranolol, you won't burn as much fat. On the the other side, lowering adrenaline will lower cortisol, so you may be able to lose fat more effectively since your body isn't in stress mode, and the body will preferably burn fat instead of muscle. A lot of people do fasted cardio and are only running on fumes and sky high cortisol, which burns all of their glycogen, and then they jump into immediately burning muscle tissue.
What kind of cardio do you do, at what intensity, and for how long?
What I find to be special about propranolol, is it can "reset" your stress response. It can break bad habits. It can retrain your body. This means you may not have to take propranolol all the time. Maybe you take it a few days, or a few weeks, or occasionally. It doesn't matter. On some level, it will modify your body's stress response to whatever stimuli known or unknown, that is creating these physical manifestations of anxiety.
You may find that you start to operate cool, collected, calm, without anxiety symptoms, even when you don't take propranolol.
You can also accomplish this "reset" with clonidine. But that's another topic. Essentially, you have to break the stress response, which is basically out of control cortisol and adrenaline, which in turn causes all kinds of blood sugar problems like hyperglycemia/hypoglycemia etc. It's a vicious cycle that has to be broken.
I think propranolol is the best solution for this and it's pretty risk free, unless you have asthma, because some people get bronchial restrictions, like wheezing etc. Not that common though.
