Sometimes you can see roundworms and tapeworms in a dogs poop if you look at the poop close enough.
Other types of worms that the dog may be infected with such as hookworms and whipworms are usually not detectable in dog poop.
When a dog is infected with worms you can sometimes even see the worms come out in the dogs vomit.
A common symptom of a dog having heartworm is coughing which gets worse as the dog becomes infected more with the heartworm.
Other symptoms of worms in dogs are loss of appetite, low energy, diarrhea, vomiting, pot bellied appearance, weight loss and dull coat.