I have written several fairly long articles on heart rate variability (HRV), and how HRV can be used to measure your overall health, but also your brain health (also check out: heart rate variability and what you can do about it, and what heart rate can tell you about your brain).
Here, I just want to introduce people who are not so familiar with heart rate variability to this subject (the one thing you want to know is that in general higher heart variability is a good thing). So check out this short video to get an introduction to the subject.
The video is meant to be simplistic, and the gritty technical details are left out - but that is too make it more straightforward. You probably only have to listen to the first 4 minutes.
(Note I am only providing this video as an information source - not to endorse the person who made the video - I have no knowledge about them. I am a bit concerned of linking to this video - but I thought the basic information was educational).