Owls will eat a small dog or cat. My neighbor back in B.C. had her small dog grabbed by an owl one night. Just came swooping down out of the night sky and that was that, not a sound, and no dog after either.
Any predator larger than a cat or dog could attack them. Often cougars, coyotes and wolves in some parts of the country will kill cats and dogs. The best thing you can do for your pets to protect them is keep them inside at night, most of the large predators are nocturnal.