I have an outside dog that someone dropped off.. he coughs, or gags constantly like he has a large bullfrog in his throat... what is this?

Heartworm or just about anything else (including something stuck in his throat).

He needs to see a Vet.

Yep, heartworm, kennel cough, murmur, there are a lot of what if's. Time to see a vet.

What's an "outside dog"?

I assuming it's a dog that lives outside and not a dog that lives indoors. For example, a dog chained to a doghouse.

That is what I'm afraid of. Aren't dogs social creatures and not to be chained up outside? And possibly he's been neglected by a previous owner, thus the cough?

Absolutely - I don't like to see outside dogs. Everyone, of course, has an opinion on the topic. I hear that they are guard dogs. Maybe they bark - but they don't do a lot of good when they're chained in the backyard and someone is breaking in the front door.

That having been said I was going to ask the OP how he/she knows this is an outside dog, particularly if it was dropped off. This could well be someone's house pet that now finds itself living outside - which is, of course, cruel.

Right on the money JKT. I was thinking "outside" as in an outsiders dog, like a stray or something. Chances are you guys are right though.

Can't spread the rep but maybe a sticky at some point about outdoor dogs isn't a bad idea.

We'll have to wait for OP to come back.

When you own certain breeds - Pits, Rotts, GSD - the "kidnapping and used for protection or fighting" thought goes through your head on occasion. I always worry that one of my dogs could end up guarding a gas station, so I take every possible precaution.