Harper was unusually restless, and she had been coughing. The 9-year-old Cavalier King Charles Spaniel loved to eat grass — her owners thought that she might have a blade stuck in her throat. But when they noticed her rapid breathing, they became concerned. This looked like something more serious. Heart disease is common in many dog breeds. It's been estimated that 7 to 8 million dogs in the United States have heart disease. It can be congenital, meaning the dog is born with