The heart is an amazing organ when we consider the work it does and how reliable it is. Its function, essentially, is to receive blood from the body, pump it into the lungs to pick up oxygen, then send it back out to the circulation system.
Sounds pretty simple for such a complex, fist sized muscle. However, it is not an ordinary muscle but one with special cells that enable it to function efficiently and reliably throughout life, all under its own nervous system.
Even though the heart is very well constructed, it can show signs of disease, especially as the body ages. These can include irregular rhythms, weakening of the muscle wall resulting in the heart growing larger, narrowing of the major vessels flowing outward from the heart, infection of the lining and valves of the ventricles, and worms, spread by mosquitoes, that live in the heart.
The most common problem to occur in older pets, however, is disease of the valves of the heart. Approximately 10% of all dogs will develop some form of heart disease during their life and 80% of those cases will be valvular disease.