I have a 5 year old schnauzer, he coughs and gags but nothing comes up. I have had him to the bet twice, NO heart worms, No kennel cough. He doesn't do it all the time but when he does it scares us. Any suggestions?

Maybe he has collapsed trachea?

Dogs with collapsed trachea will cough and gag and sound like they have kennel cough.

A good way to find out would be for an x-ray.

Heart disease is another thing that will cause a dog to cough and gag. To find this out would be with an x-ray.

Allergies?