The Cavalier King Charles Spaniel is perhaps the largest toy breed: though historically a lap dog, modern day fully-grown adults tend to fill a lap rather amply. It is nonetheless quite small for a spaniel, with fully-grown Cavaliers roughly comparable in size to adolescents of more conventional spaniel breeds. Breed standards call for a height between 30 and 33 cm (12–13 inches) with a proportionate weight between 6 and 10kg (10 and 18 lb), although even purebreds commonly grow to 35-40 cm tall with a proportionate weight between 20-25 pounds. Unlike most other spaniels, the Cavalier has a full-length tail, well-feathered with long hair, which is usually not docked, which is typically carried aloft when walking.
The breed is highly affectionate. Most dogs of the breed are playful, extremely patient and eager to please. As such, dogs of the breed are usually good with children and other dogs. A well-socialized Cavalier will not be shy about socializing with much larger dogs. (However, on occasion, this tendency can be dangerous, as many cavaliers will presume all other dogs to be equally friendly, and may attempt to greet and play with aggressive dogs.) Cavaliers will adapt quickly to almost any environment, family, and location. Their ability to bond with larger and smaller dogs make them ideal in houses with more than one breed of dog as long as the other dog is trained. Cavaliers are great with people of all ages, from children to seniors, making them a very versatile dog. They rank 44th in Stanley Coren's The Intelligence of Dogs, being of average working/obedience intelligence.
The extremely social nature of the Cavalier KC Spaniel means that they require almost constant companionship from humans or other dogs, and are not suited to spending long periods of time on their own. (Even though they will be very patient and obedient) This breed is one of the friendliest of the toy group. It is important for Cavaliers to have a hand-reared puppyhood to ensure security and friendliness. When they greet somebody they tend to lick them on the hand. They connect with their owners almost immediately, but are rarely a little delayed with strangers. They are very playful.
Some Cavaliers have been known to exhibit traits in common with cats, such as perching in high places (the tops of couches, the highest pillow, etc), cleaning their own paws and can also show some birding qualities. Cavaliers have been seen to catch small birds in mid-flight that are flying too close to the ground. Such behaviour is a result of their earlier use as a hunting dog, and as such, they can develop habits that predispose them to chase small animals such as chipmunks, squirrels, rabbits, birds etc. Because of this, it is recommended that care should be taken when walking a Cavalier off-leash, as they can single-mindedly chase a butterfly or rabbit onto a busy road or other dangerous situation without regard for their own safety if not properly trained.
Cavaliers can suffer from a number of severe genetic defects. Unfortunately, two possible genetic conditions, mitral valve disease (MVD) and syringomyelia (SM), can be both severe and very common. Breeders who breed for health will screen their breeding dogs for heart, syringomyelia, hip, eye, hearing, and patella problems and follow recommended breeding protocols to try to reduce the incidence of all these defects in the breed.
Mitral valve disease
It is very common that Cavaliers eventually suffer from mitral valve disease, with heart murmurs which may progressively worsen, leading to heart failure. This condition is polygenic, and therefore all lines of Cavaliers worldwide are potentially susceptible. It is the leading cause of death of the Cavalier King Charles Spaniel and the reason the breed's expected life span is only between seven and ten years.
Hip dysplasia
Hip dysplasia (HD) is a genetic disease that affects up to a third of Cavalier King Charles Spaniels. It is never present at birth and develops with age. Hip dysplasia is diagnosed by x-rays, but it usually does not appear in x-rays of Cavaliers until they mature.
Keratoconjunctivitis sicca
A common disorder among Cavaliers is keratoconjunctivitis sicca, colloquially known as "dry eye". The usual cause of this condition is an autoimmune reaction against the dog's lacrimal gland (tear gland), reducing the production of tears. According to the Canine Inherited Disorders Database, the condition requires continual treatment and if untreated may result in partial or total blindness. This disorder can decrease or heal over time. If treating with the ointments vets prescribe, careful attention to the dog's eyes should be paid, as they can be under- or over-medicated.
