This is a condition in which the esophageal muscles lose their strength and the esophagus dilates to a much larger size. Usually dogs with this condition regurgitate food as well as water but I have seen at least one other dog that started out just regurgitating when it drank water. Sometimes the enlarged esophagus is visible on plain X-rays of the chest but often it is necessary to use some kind of contrast medium like barium to make the enlargement visible.

There are other possible problems like esophageal diverticuli, hiatal hernia, esophagitis, pylorospasm, esophageal tumours and probably others. In addition, there are about thirty disorders that can cause a secondary megaesophagus problem.