This is a premise for a boring chapter of a gag manga. Boggles the mind to see it played so dramatically.
I dont think the heartbeat thing is a strictly illegitimate beat for the comic to hit - I've said in a bunch of these threads that I think its good when the comic acknowledges that, yes, mizuhara does actually feel anything about kazuya bc that needs to be true for it to be a functional romance story. But the heartbeat thing is also insane. How is that the corner we've been boxed into, where the only moments of understanding between the two romantic leads have to come from base physiological responses instead of, like, interactions they have as characters.