Andrew Huberman· PhD
it's that exhale slowing your heart rate down that's mediated by the vagus nerve now there's a more thorough description of that which I'll just give you now and it's not that lengthy so here's how it goes when you inhale your diaphragm actually moves down and as a consequence your heart actually gets a little bigger it has a little more space as a consequence the fluid in your heart moves a little more slowly per unit volume and there's a neural signal to speed the heart up conversely when you exhale the diaphragm moves up that means there's a little less space for the heart in the general area where it's sitting so the heart gets a little bit smaller a little more compact that means that the fluid in your heart is moving more quickly through that smaller space and there's a neural signal mediated by the Vagas to slow the heart down so that's why inhal speed your heart up and exhales slow your heart down that is the basis of so-called RSA or respiratory sinus arhythmia