Chronic valvular disease can be thought of simply as 'leaky valves', caused when the moving parts of the heart valves thicken and harden with age. The result is more or less the same as when a valve in your central heating system starts to wear out: increasingly poor circulation.

This illustration highlights the various valves in the heart that can be affected by disease.

These valves may thicken or harden with age. This can either restrict bloodflow, or allow blood to 'leak' back past the valve.

If any valve is affected in this way, it will compromise the heart's ability to pump blood.

Although valvular disease can affect any dog, smaller breeds tend to be more prone. In particular, the Cavalier King Charles, Chihuahua, Miniature Schnauzer, Maltese, Pekingese and Whippet. Of these, Cavalier King Charles Spaniels tend to develop the disease earlier in life.