 Being a brachycephalic breed , King Charles Spaniels can be sensitive to anesthesia . This is because in brachycephalic dogs , there is additional tissue in the throat directly behind the mouth and nasal cavity , known as the pharynx , and anesthesia acts as a muscle relaxant causing this tissue to obstruct the dogs ' narrow airways . These narrow airways can decrease the dogs ' ability to exercise properly and increase their susceptibility to heat stroke . Other congenital and hereditary disorders found in the King Charles Spaniel are hanging tongue , where a neurological defect prevents the tongue from retracting into the mouth ; diabetes mellitus , which may be associated with cataracts ; cleft palate and umbilical hernia . The English Toy Spaniel Club of America recommends that umbilical hernias be corrected only if other surgery is required , due to the risk of surgery in brachycephalic breeds . In another study conducted by the OFA , the King Charles Spaniel was the 38th worst of 99 breeds for patella luxation ; of 75 animals tested , 4 % were found to have the ailment . However , surveys conducted by the Finnish breed club between 1988 and 2007 found that the occurrences were higher in some years , ranging from 5 @.@ 3 % to 50 % . 
