In principle, the Cavalier King Charles Spaniel is a robust dog that is not very susceptible to illness. Regrettably, due to back breeding with an extremely small breeding base, some members of the breed suffer from some hereditary diseases. The diseases mainly affect the heart and nerves and affect a large proportion of the population. Heart disease is more common as you get older, but you can reduce the risk with a healthy diet. Some Cavaliers suffer from spontaneous muscle spasms caused by neurological dysfunction. However, today’s breeders usually make sure that they only mate healthy four-legged friends in order to slowly eradicate hereditary diseases.