Mitral valve disease constitutes about 75% of heart diseases in dogs. The mitral valve is the heart's main pumping chamber. When it's not working properly, eventually this leads to congestive heart failure.
A large clinical trial evaluated effectiveness of using pimobendan to delay the onset of clinical signs of congestive heart failure in affected dogs.
The results seem promising.
Treatment of Canine Mitral Valve Disease Shows Promise
Mitral Valve Disease in Dogs