Mitral Valve Disease
Mitral valve disease is the most common heart disease in all breeds of adult dogs but the incidence is much higher in the Cavalier King Charles Spaniel. Though a Cavalier is more likely to develop mitral valve disease at a younger age than other breeds the deterioration rate is only slowly progressive and their life span would be similar. Males are 1.5 times more prone to develop mitral valve disease than females.
Here are a few links to research and information about heart disease in the Cavalier King Charles Spaniel.