
Hi
Unfortunately the statistics are approximately 50% of all cavaliers have MVD (Mitral Valve Disease) by age 5, and around 99% by age 10, so yes, it is more or less inevitable. There are lots of articles and info on this website:
http://www.thecavalierclub.co.uk/It doesn't mean your dog will necessarily die young though as it varies a lot on how severe the problem is. Badly bred dogs have been known to die aged just 5 or 6, but the wellbred dogs from caring and responsible breeders can have pretty normal lifespans with care. The best we can hope for is for it to develop as late as possible in life, and as such it is important that the parents of any pups were at least 2 ½ years old and heart clear (all breeding cavaliers should be tested every year) and that THEIR parents in turn were at least 5 years old and still clear. Did the breeder show you the parents certificates? Told you about grandparents? On the website I've given there is a list of Cavaliers aged over 5 and still clear, you can look for your dog's relatives there. (It does however NOT mean all of those dogs are STILL clear, it just means they were clear at the date given so did not develop MVD EARLY. My own dog is still on there and he is NOT clear now.)
I've had 4 Cavaliers. One died on her first birthday of other reasons. One developed the murmur aged just under 4, and the ther two were clear until 7 years of age. Casey the Triclour now lives with my mother in law, he is almost 10 and his heart isn't too bad -but he is grossly overweight so he suffers a lot more than from his heart than he would have done was he slim and the vet has said many a time that if she only slimmed him down he'd be really well. So his heart is pretty good as he is still alive.
Rufus my blenheim developed his heart murmur aged 7, it came all of a sudden and was severe at once. He's been on heart medication ever since. The vet told us he would not live to see Christmas 2002, but he's still here aged 11 ½! He needs a lot of extra care and we know he could go at any time but he's very happy and knows his limits so we let him do pretty much what he himself feels capable of.
I must admit I will not get another Cavalier due to all the health problems, but there is a DNA test being developed so one day in the future we will be able to tell at birth if a cavalier will be affected by MVD and/or Syringomyelia, the other major problem, or not. When that happens I will get another. :)