Normally I wouldn't attack something that someone else feels is helping (even placebos can be helpful for some people), but this is the top comment.
Maybe breathing in a consistent rhythm to get a coherent heart rate variability (HRV) is the sole magic behind meditation, HeartMath, etc?
Here is a good TEDx talk by Alan Watkins on HRV: https://youtu.be/Q_fFattg8N0 (there is also a part 1, but part 2 has the good demo)
I believe the "coherent" HRV curve they claim brings all these benefits is simply the effect of respiratory sinus arrythmia (why your heartrate decreases when you breathe in) while breathing at a very regular interval—the HRV curve just happens to be a good indicator of how regularly you're breathing.