Endocardiosis of the canine mitral valve is a chronic degenerative disease of the valve between the left atrium and the left ventricle of the heart. This condition is more commonly referred to as Mitral Valve Disease, or MVD. Deposition of mucopolysaccharide in the valve and its attached cords causes the valve to become distorted, allowing blood to leak back into the atrium during contraction of the ventricle. Most of the time, the mitral valve is the only valve affected by endocardiosis, but in approximately one-third of the affected dogs, the tricuspid valve (between the right atrium and right ventricle) will be affected as well. Diagnosis is most typically made by auscultation. The murmur of MVD is typically heard best at the left fifth intercostal (between-the-rib) space. Murmurs are generally rated as grade one (I) through grade six (VI), depending on the loudness of the murmur. As the disease progresses, the murmur typically becomes louder. In a very young dog with a very soft murmur, further studies may be necessary to determine the source of the murmur.
All murmurs are not indicative of MVD; innocent flow murmurs sometimes appear in young, healthy dogs. A Doppler study will document regurgitation into the left atrium, and may be recommended in a young-breeding animal with a murmur. Doppler studies are also being used in some areas, since regurgitation of blood will most likely be seen on Doppler before it is heard as a murmur.
The veterinary and genetic communities agree that there is a genetic basis for MVD, and therefore the key to decreasing the incidence of MVD lies in selective breeding. To this end, a yearly heart examination is recommended, carried out by a board certified canine cardiologist.
MVD is not only inherent to Cavaliers bred in the USA. Studies have been ongoing in other countries including Great Britain and Canada. Statistics show that this is a health problem which can affect Cavaliers everywhere. Importing your Cavalier from another country does not necessarily mean, you are getting a healthier or better dog. It could be quite the opposite.
If a breeder tells you that their lines are free of MVD or other genetic diseases or that these problems only show up in dogs from other countries, I suggest you walk away from him or her. He/she is not being truthful with you. Any breeder who is honest and has bred for any length of time will tell you that problems can and do arise even with the best breeders. Trust the ones who are honest with you and will tell you how they work within their breeding program to eliminate these problems. These breeders constantly test, reassess, study, show and learn as much as they can about their dogs and the breed. Also, they can prove to you their testing by showing you the test results. They will honestly talk about the problems in their lines.