Heart disease in dogs is a common complaint. The most common cause of canine heart disease is degeneration of the valves within the heart. This is commonly called degenerative valvular disease, valvular insufficiency, valvular regurgitation, endocardiosis or chronic valve disease.
The Basics of Degenerative Valvular Heart Disease
All dogs have valves within the heart that help regulate the flow of blood from one chamber of the heart to another. When the valves are of a normal shape, they function to direct the flow of blood from the atria to the ventricles of the heart.
In some dogs, these valves become misshapen. Often, the valves become thicker than normal and take on a nodular appearance. As the valves become more abnormal in their shape, the seal that is formed between the heart chambers when the valves are closed is no longer tight and the valves become leaky, allowing blood to flow backwards. This means that instead of all of the blood flowing from the atria to the ventricles as it normally should, some of the blood flows backwards and reenters the atria.
Mitral Valve Disease is the Most Common Form of Heart Disease in Dogs
The valve that is most commonly affected is the mitral valve. The mitral valve is the valve that is on the left side of the heart. It sits between the left atrium and the left ventricle and regulates the flow of blood between these two chambers.
When the mitral valve degenerates, some of the blood that should move through the left ventricle into the aorta (the large blood vessel that leaves the heart) flows backward into the left atrium instead of entering the aorta.
As the blood volume increases in the left atrium and ventricle, both the left atrium and the left ventricle begin to increase in size. As the chambers of the heart reach their maximum size limits, the pressure inside the chambers starts to increase as well. This results in fluid leakage into the lungs, known as pulmonary edema or congestive heart failure.
A heart murmur will occur in dogs with mitral valve disease as well. This will be audible by your veterinarian when your dog is examined and a stethoscope is used to listen to his heart. The heart murmur is caused by the regurgitation of blood through the leaky valve.
Mitral valve disease is especially common in small breed dogs though it can occur in large breed dogs as well. Some breeds are more commonly affected than others. These breeds include:
- Miniature poodles
- Cocker Spaniels
- Miniature Schnauzers
- terrier breeds
- Cavalier King Charles Spaniels
Cavalier King Charles Spaniels often develop this type of heart disease at a younger age than many other breeds and the disease may also progress faster for this breed than for others.
Signs of Heart Disease Caused by Mitral Valve Degeneration
The signs caused by a degenerating mitral valve are those of congestive heart failure. The most commmon signs seen are:
- increased respiratory rate
- exercise intolerence
- lack of appetite
The severity of signs will vary depending on the extent of the disease. Some dogs may have a heart murmur but exhibit no other signs of heart disease. Others may develop a mild cough that does not interfere with their quality of life. Still others may develop much more serious signs which may even become life-threatening if left untreated.
In some dogs with mitral valve disease, the tricuspid valve (the valve between the right atrium and ventricle) may also be diseased. This may lead to additional signs of heart disease such as a swollen fluid-filled abdominal cavity and fluid accumulation within the chest cavity.