Since , it has grown in popularity in the United States and ranks as the 19th most popular pure-breed in the United States. Since they are family dogs, it is recommended to not leave one alone for long periods at a time. The expected average lifespan of a Cavalier King Charles Spaniel is under ten years. The Cavalier King Charles changed dramatically in the late 17th century, when it was interbred with flat-nosed breeds. Until the 's, the Cavalier shared the same history as the smaller King Charles Spaniel.
The Cavalier King Charles Spaniel is an elegant, royal, toy spaniel, slightly longer than tall, with moderate bones. The Cav retains the build of a working spaniel, yet in a smaller version. Their gait is free and elegant, with good reach and drive. Their silky coat is of moderate length, with a slight wave permissible. Long feathering on the feet is a breed characteristic. A hallmark of the breed is its gentle, sweet, melting expression.
In its heyday, this breed was known as a 'comforte dog' and doctors even wrote prescriptions with this little dog as the remedy. The original Cavalier King Charles was developed from the toy spaniels pictured in the work of 16th, 17th and 18th century painters such as Van Dyck, Titian, Stubbs and Gainsborough. These portraits show a small spaniel with a flat head, high set ears, almond shaped eyes and a pointed nose. Another job the dogs had was to attract fleas off their mistresses so that the owner would not get bitten and die of the plague. The royal name, 'King Charles Spaniel' was bestowed during the reign of King Charles II, who was so fond of his spaniels he could not be parted from them.