Heiji pushed the button at the same time as Sasuke.

"Be ready for anyth--" he said, just before gas started pouring into the room. He held out for a little while, sure, long enough to grab his cloth bag and dunk it in his water bottle to serve as a makeshift mask to offer to Sasuke.

But then he'd just kind of crumple to the floor and remain out for at least half an hour. Awesooome.