Thanks for the chapter :D
"My heart's about to burst!"
Yes, and it's no longer the running, but the hand-holding that is causing this. Progress!
This just made me realize how many things this series has set up over time. Every time Ayumu is forced to run, she feels out of breath and her heartbeat becomes crazy. Well, guess what, these also happen to be symptoms of love!
This specific thing aside, we've seen so many other gags develop, vary, or gain significance. Ayumu's disliking of crowds (but she loves the aquarium date), Hayami's obsession with running (which she picked up from her mother), just to name a few off of the top of my head.