A good reply from Bev.
We all have had different experiences but many of us have at least one dog with SM and most of us eventually have them with MVD.
The single best thing you can do is only ever get a puppy from a breeder who has properly cardiologist tested her breeding dogs and follows the MVD breeding protocol, who MRI screens and follows the SM protocol; and does other needed tests (eg s/he should have done DNA tests to know if there is EFS in her dogs; also eyes should have been checked, ideally, hips and knees checked too). No cavalier should ever be bred before 2.5 as the most serious conditions, MVD and SM are hereditary and progressive.
Unfortunately both these conditions are considered endemic -- eg very widespread. Close to 100% will eventually have MVD by age 10, half have it by age 5 or 6. A sample of over 500 cavaliers indicated about half will have SM by age 5; and about 70% by age 6-7. There's very good evidence that following the protocols and properly testing greatly reduces incidence
and increases the age of onset, when a dog does get either disease. That said many with SM and MVD can simply live with the conditions in a mild form and may not need meds. Each dog is different.
As MVD is progressive, almost all cavaliers will be heart clear for the first year or two of life, which won't tell much about the dog's future. Incidence in parents, grandparents and siblings is a better indicator, and whether the breeder followed health protocols and tested properly.
Sadly this is an illness prone breed. There's a high rate of many problems, including hip dysplasia (according to statistics cavaliers have a higher rate than several giant breed dogs...) and knee problems are more common generally in
all small breeds. Dogs with genetically altered noses (to be shorter) and enlarged eyes are more prone to both respiratory and eye problems, so these are structural issues in the breed because of the way cavaliers look (other breeds & mixes with similar alterations also can have these issues). There are some cavalier-only problems like Episodic Falling (EFS) and Curly Coat/Dry Eye, but there's now a DNA test for both together
, that all breeders should be using.
The breed also has a high propensity to the dog equivalent of glue ear (PSOM). This shows up frequently when dogs are MRId for SM. It can sometimes cause similar symptoms, sometimes none. It likely often causes some degree of deafness -- one reason why this breed has a very high rate of deafness, but there's also congenital deafness as a separate issue.
It's a lot of things for one small, lovely breed, and that's why raising awareness about, and funds for, breed health, and also giving people resources on how to choose a breeder, has long been a focus of the board.
I've had five cavaliers. Of those, three have CM/SM, three MVD (onset by around age 7), four have PSOM, and all five are deaf to some degree (two were/are almost stone deaf). All were losing hearing by about age 7, which doesn't inhibit them but does make for more careful management. The SM dogs are managed on meds. Fortunately they have not been severely symptomatic, but one is one a high level of painkillers at age 10. I lost one cavalier to MVD -- truly the worst condition I have had to manage.