Was that Nick Castle doing the heavy breathing or was it later dubbed in? Also curious why it wasn’t in the sequel, it adds a menacing aspect to him that I think fits well.
Curiously I don’t recall hearing or reading anything about the breathing in the film, a wealth of knowledge exists about it but not that lol.
As for the sequel he can be heard breathing but it was lower and more relaxed, not the bursts of audible breathing we hear in the first like in the closet attack, more like what we hear at the end before the credits.
I’d bet on dubbing, the mic likely couldn’t pic up on the breathing with that kind of volume. It’d be interesting if the dubbed breathing wasn’t Castle.
lt would have been dubbed in after/editing. As it was just the camera making it seem like his perspective. They would have added that in afterwards along with/around the same time they chose what piece of music went with what scene. As to who’s breathing? I would say John or Tommy Lee or somebody close to the editing part of the movie unless they had Nick come back in & start breathing into a mic.
It’s there…I had no probs hearing it today. I remember hearing the difference between the 2 when only Halloween II was stereo.
TLW did the Doctor Dimension voice so I’m betting it’s him 
If you’ve ever heard his voice, the breathing and the grunts sure do sound like him.
http://www.youtube.com/watch?v=Gq6KWyJXpqI
There was louder breathing in the TV cut of H2, don’t forget. But as for H1, yeah It could be any one of the bigger honchos making the film.
I think the scene when I really heard it was when he stabs the bf up against the wall before the famous head tilt.
The breathing during his kills is definitely not added in any of the later ones.
Why would they take the breathing effect from the shape, I also miss the grunting …it gave the shape this dark dimension
I liked that. Gives Myers a whole new dimension. He’s no robot. He’s human. Well in the first two movies he was. Haha!
Most likely dubbed later… 
I miss the breathing, it made him sound monstrous, my friend watched Halloween for the first time, and was freaked by the breathing, especially at the end. She missed it in the later films.
Definitely feel the breathing was a good addition. Maybe if there’s ever another remake they could include it.