Cavaliers are little spaniels with a lot of energy. But like most dogs Cavaliers also can suffer from some deseases specific to them (and also some other breeds).

The most serious health problems are the MVD-mitral valve desease (a hearth desease), and syringomyelia - SM ( a neurological desease). Although they can also suffer from hip dysplasia, luxating patellas and some eye problems, common also in other breeds.

If You are interesed in some more reading, there are some informative links listed below:

General health:

http://www.cavalierhealth.org/
http://www.aboutcavalierhealth.com/
http://www.cavalierhealthfoundation.com/
http://www.ckcs.com/about/health.html

SM:

http://sm.cavaliertalk.com/

a genetic study

If you are interested in buying a cavalier I would suggest that you buy from a breeder that is testing his cavaliers for MVD (ultrasound and Doppler), and that his cavaliers have their eyes and patellas examined by a veterinary. You should see the test results, don`t just believe the breeder. It is also not enough if the breeder tells you that his cavaliers are healthy and they don`t need the tests.