My dog ate some of my household plant, Philodendron. He has been throwing up and gagging...sounds like he is choking. At times he has real heavy breathing. When he relaxes he doesn't gag or cough...but, as soon as he is disturbed he starts again. He has been going to the bathroom outside but is not interested in eating.
This plant can irritate mouth and throat.
I would see your vet with him. He may need fluids and other supportive care to get over this.
Hope this helps you!