Heart Disease in Dogs

The heart has four chambers. The upper chambers are called atria (singular: atrium) and the lower chambers are called ventricles. In addition to the upper and lower chambers, the heart is also considered to have a right and left side.

Blood flows from the body into the right atrium. It is stored there briefly before it is pumped into the right ventricle. The valve between the right atrium and right ventricle is the tricuspid valve. The right ventricle pumps blood into the lungs, where it receives oxygen. It then flows from the lungs into the left atrium and is held there before going into the left ventricle. The valve between the left atrium and left ventricle is the mitral valve. The left ventricle contains the largest muscle of the heart, which pumps blood out to all other parts of the body.

Heart disease in dogs falls into two categories: congenital and acquired. Congenital heart disease accounts for less than five percent of all canine heart disease and is generally diagnosed when the dog is very young. The vast majority—95 percent—of heart disease cases are acquired. Acquired heart diseases include those that a dog naturally acquires during his/her lifetime, usually as a result of normal wear and tear, infection, or injury.

Acquired heart disease is further subdivided into disease with a valvular cause and disease with heart enlargement. The majority of dogs with acquired heart disease are afflicted with degenerative valve disease (also known as myxomatous valve disease or valvular insufficiency) or dilated cardiomyopathy. The remaining causes of acquired heart disease is caused by a group of other conditions, such as heartworm infection and endocarditis (heart valve infection).

Degenerative valve disease, or DVD, is the largest category of heart disease veterinarians see. Degenerative mitral valve disease is more common than tricuspid valve disease, however dogs can have both sides affected too. Within this group, about 10 percent of dogs between the ages of 5 and 8 are affected, as well as 20 to 25 percent of dogs between the ages of 9 and 12 and 30 to 35 percent of dogs over 13. Smaller breeds are more likely to be affected by DVD, and certain pure breeds are especially susceptible. These include the Boston terrier, Cavalier King Charles spaniel, Chihuahua, miniature pinscher, miniature and toy poodle, Pekingese, and Pomeranian.

In a case of DVD, the valves of the heart do not seal properly, allowing blood to leak backward into the left or right atrium. This causes a heart murmur which can be heard. The valve leakage increases the load on the heart, which is not able to adequately pump blood to the rest of the body and may become enlarged from the excess blood. DVD is a degenerative progressive disease.

The earliest sign of a leaking mitral/tricuspid valve is a heart murmur. This is produced by the turbulence created when some of the blood goes backward through the leaking valve and into the left or right atrium. A murmur does not mean that heart failure is imminent, but as time goes on, the leak may become more severe as more and more blood travels backward into the left/right atrium. This results in reduced pumping efficiency and, eventually, congestive heart failure. From the time a murmur develops, it may be a few months to several years until heart failure occurs. Some dogs also have heart murmurs but never develop congestive heart failure. 

Common signs noticed at home with heart disease are coughing, decreased activity or tiring easily with activity, or sometimes collapse. 

Congestive heart failure (CHF) means that the heart is not pumping normally. When the heart isn’t pumping effectively, fluid will begin to backup either in the lungs or the abdomen depending on the side of the heart that is backing up. With mitral valve disease (most common), the fluid backs up in the left atrium and then backs up further to the lungs, called left-sided congestive heart failure. With tricuspid valve disease, the fluid backs up in the right atrium and then backs up further to the abdomen, called right-sided congestive heart failure. Signs of congestive heart failure would be a wet cough, fast breathing,
or difficulty breathing, or a distended abdomen, depending on the side of the heart affected.

Dilated cardiomyopathy, or DCM, affects the heart muscle itself. The weakening of the heart’s muscle hinders its ability to contract, which means blood is not pumped efficiently throughout the vascular system. The heart becomes weak and enlarged, which further impairs cardiac output over time. DCM has a quick onset, progresses rapidly, and produces dramatic effects. All four chambers become enlarged as the heart muscle stretches and thins out. 

DCM primarily affects middle-aged dogs typically from a genetic disorder. Large and giant breeds are most susceptible to DCM, including Doberman Pinscher, Boxers, Great Danes, Golden Retrievers, and Cocker Spaniel. There are also dogs affected due to a nutritional deficiency with taurine. There has also been a link found between grain-free diets and DCM, usually diets containing pea proteins and potatoes, in dogs that are not genetically predisposed. 

Congestive heart failure can also occur with DCM from the heart muscle tiring and not pumping effectively, so that fluid backs up. It backs up similarly to the CHF from valvular disease, but the valve in this case isn’t the cause of the fluid backup. DCM can also cause arrhythmias, or abnormal heart rhythms, due to the stretching of the heart muscle. This can be mild or severe and in some cases, even fatal. 

DCM is not the most common cause of heart failure in dogs in general. However, it is the most common cause of heart failure in large breed dogs. Small breeds are only occasionally affected, unless they are on grain-free diets.

DVD or DCM develop over many months or even years. Its effects on blood flow also develop slowly. As heart function declines, the body is able to compensate for several weeks or months. However, at some point in time, the body’s ability to compensate is no longer effective and the animal goes into severe heart failure in what appears to be a matter of hours. Rapid, heavy breathing, a blue tongue, excessive drooling or collapse may be the first signs.

There are several tests that are used. All provide valuable information while determining different aspects of heart function.

The combination of all of these tests gives us our best evaluation of the dog and his/her heart function. However, if cost considerations prohibit every test, even two or three will provide valuable information.

Yes. Treatment centers on eliminating signs of congestive heart failure. We commonly use drugs, such as diuretics, ACE inhibitors, and pimobendan (which helps the heart pump more efficiently), to correct these signs. Pimobendan is a medication that can also be started in some cases with moderate heart disease before heart failure occurs to delay the progression. 

If a dog has a sudden onset of heart failure, rapid administration of the proper drugs is essential to survival. Treatment is based on a clinical presentation of each individual patient. Commonly used drugs include diuretics, ACE inhibitors, and anti-arrhythmic medications if indicated. In nutritional DCM, specific supplements are prescribed.

There are many factors that must be considered before that question can be answered. The results of the tests are important and the response that occurs within the first few days is another indicator. If a response does not occur within a few hours to days, the prognosis is typically not good. These conditions will progress, but the rate at which they will progress in the future is variable and difficult to predict. Once heart failure does occur, the average prognosis is 6 months to 2 years with medications.