These included the unsuccessful Toy Trawler Spaniel and the now popular Cavalier King Charles Spaniel. These included the unsuccessful Toy Trawler Spaniel and the now popular Cavalier King Charles Spaniel. The Cavalier is slightly larger, with a flat head and a longer nose, while the King Charles is smaller, with a domed head and a flat face. Heart conditions related to the King Charles Spaniel include mitral valve disease, in which the mitral valve degrades, causing blood to flow backwards through the chambers of the heart and eventually leading to congestive heart failure. 'RSPCA Pulls Out of Crufts Over Breeding Row'. The Times.