alt Hacker NewsNot saying "cardiorespiratory fitness" and "heart rate" are 1:1, because they're certainly not, but beta blockers are a known treatment for certain kinds of anxiety. I can attest that taking low-dose propranolol twice a day (without pulling any other levers related to lifestyle, stress, etc.) has helped me mellow the fuck out, which I sorely needed lol. So I would wager that cardio fitness is itself correlated with anxiety and anger, although in practice it's tangled up with many other factors.
In addition to baseline heart rate, there's also some interesting stuff related to anxiety and heart rate variability. My understanding is that certain types of breathing exercises improve HRV in the short term, which is good for calming down if you're riled up, but people with good cardio health have a better baseline HRV in the first place. (Also, this has always been unintuitive to me, but higher variability is better for anxiety, not lower variability.)
I've been doing my own personal research on HRV and getting to the bottom of it.
The literature is bewildering because of course there are many ways to measure it. If you measure it over the course of the day it is influenced by things like the activities you do. Of course your HRV is going to be higher if you alternate intense activity that raises your heart rate with rest and since activity is so important in it I don't think it is fair to look at a whole day trace.
I think the most important phenomenon is
https://en.wikipedia.org/wiki/Mayer_waves
which are associated with the metric RMSSD as described here:
https://en.wikipedia.org/wiki/Heart_rate_variability
This is called "SD1" in my app
https://gen5.info/demo/biofeedback/
You can use that app to increase the amplitude of your Mayer wave, what you do is breathe in when you see the wave going down and breathe in when you see the wave going up. It is a little tricky if your Mayer waves are initially weak and you might feel light-headed and think "I can't breathe" but once it settles in it is a very strong effect.
I have read a number of patents for HRV biofeedback and they all involve much more complex things that you might think would work if you hadn't tried it but that I don't believe would work having tried it.
Funny I have been taking Nebivolol, another beta blocker, and found that it drastically lowers HRV-inferred stress as measured by my Garmin watch -- I can't really say how it affects my app because I wrote it after I started on the drug.