I'm surprised you got a beta-blocker instead of something like Florinef. I'd ask your doc if your high HR on standing or walking, but NOT resting could be the result of low blood volume.
A tachycardia med (it was a calcium channel blocker for me) did nothing for my symptoms. The Florinef, however, made a big difference -- reducing that big change in HR from resting to standing/walking. My resting HR was still high, though, so we added back the tachy med which
then helped.
In my case the issue was my heart beating really fast in an effort to get more blood to my upper body and brain. Stopping it from doing that with a tachy med was not a good thing. Getting enough blood volume meant my heart did not have beat so hard to keep my brain working. That was a much better solution.