I’m no bio-person (didn’t take a single biology course in high school) nor a yogi bear but I’ve noticed in the past that breathing in actually prompts a noticeable increase in heart-rate when compared to breathing out.
The reason I know is because I got a fit-bit [ripoff] as a gift and wanted to test it out, but manually feeling my pulse when I was trying to get below fifty BPM led me to this observation kek.