Why does my dog vomit and breathe hard?

These could be symptoms of many conditions, including an obstruction of the trachea, an internal injury, or an infection of the lungs. These are also classic symptoms of a heartworm infestation. All of the above are life-threatening , so please take your dog to a veterinarian for a complete examination as soon as possible. Even if the problem turns out to be a relatively minor one, such as kennel cough, it's best to play it safe.