Many newly qualified Veterinary Surgeons appear not to recognise the difference between the King Charles Spaniel and Cavalier King Charles Spaniel.
These are two entirely different breeds having entirely separate Breed standards and identities. While the King Charles Spaniel has its origins in the courts England and France in the 15th Century,The Cavalier King Charles Spaniel only became a recognised breed in the early part of this century(1945 ).
In 1998 there were only 221 King Charles Spaniel puppies registered with the Kennel Club in the UK while the registrations of Cavalier King Charles Spaniels puppies exceeded 13000. The media often incorrectly describe most Cavalier King Charles Spaniels who are pictured in magazines and newspapers as being King Charles Spaniels.
It is very alarming for the new owners of King Charles Spaniels when first attending a Veterinary Surgery to be told that their beautiful King Charles Spaniel is an extremely bad specimen of a Cavalier King Charles Spaniel.
Several of the reasons that have been quoted are as follows -:
1) Because the dog has a domed head it most probably has Encephalitis-( Water on the brain )
2 - Because the dog has an undershot jaw it may need corrective surgery.
3 - Because the dog has fused nails and pads it may need future surgery.
All these "faults "are part of the King Charles Spaniel Breed Standard.

To quote from the two different breed Standards

The King Charles Spaniel	The Cavalier King Charles Spaniel
Distinctive Domed head full over eyes	Skull almost flat between ears
large wide open nostrils very short and turned up to meet skull	Shallow stop length from base of stop to tip of nose about 1 ½
Bite should be slightly undershot	Jaws strong with perfect regular and complete scissor bite
Compact well padded and feathered 0ccasionally central pad and nails fused	Compact cushioned and well feathered
King Charles are generally smaller between 8 and 14 lbs	Cavaliers are usually larger between 12 and 18 lbs
Four colours Blenheim Tricolour Black and Tan and Ruby	Four colours Blenheim Tricolour Black and Tan and Ruby .