Not sure if this is the same thing but when Mack was a puppy, he would snort a lot when he got excited (mainly when I got home from work and took him out of his crate) - and a handful of times, he threw up some foam. I have read that it may be due to their short snouts - sort of the breathing problems that pugs have. I try and calm him down during his snorting fit and once he has calmed down, the snorting no longer occurs. Not sure if Mack's snorting is the same as the heaving you are describing. He doesn't do the snorting as often now since he's older but when he is super-excited, he does still snort.
Oh! And after Mack was neutered, he did throw up that night. It was because of the anesthesia he had for the procedure. This is also common for humans as well.
Hope that helps,
~Steph & Mack