Heart Disease in Dogs

By Tammy Hunter, DVM

What types of heart disease do dogs get?

Heart disease is a serious medical condition in dogs, cats, and humans. In general terms, heart disease in dogs can be divided into two categories: congenital and adult onset.

In congenital disease, the heart defect is present at birth. Signs of congenital disease are often seen at a young age, but in some cases, it can go undetected for many years. Congenital heart disease may be caused by a developmental problem that causes malformation of the heart as the embryo develops. This type of congenital heart disease may affect only a single pup in the litter. It may also involve a genetic or hereditary disorder, in which case the problem may develop in more than one pup in the litter.

Most adult-onset heart disease occurs due to degeneration of the mitral valves over time, resulting in abnormal function. Some adult-onset heart disease can be due to a hereditary condition that progresses as the dog ages, eventually causing problems. The cause of most types of adult-onset heart disease is unknown, although genetics and lifestyle (weight, physical activity, and diet) may play an important role.

What is the structure of the heart and how is it affected by heart disease?

The heart can be divided into four functional components:

  • the heart muscle, which pumps the blood around the body,
  • the heart valves, which act to prevent the blood going in the wrong direction,
  • the pericardium, which is a tough membrane surrounding and protecting the heart, and
  • the electrical conducting system which initiates and transfers electrical impulses around the heart, allowing it to contract or beat in a systematic and coordinated fashion.

Heart disease can affect any or all of these parts.

How common is heart disease in dogs?

Heart disease is more common in dogs than in cats. Approximately 1 in 10 dogs will develop heart disease in their lifetime. The two most common types of heart disease in dogs are  mitral valve disease and dilated cardiomyopathy or DCM (disease of heart muscle).

Mitral valve disease results from a degenerative thickening of the mitral valve between the upper-left heart chamber (left atrium) and the lower-left heart chamber (left ventricle). Blood flow becomes turbulent as blood leaks backwards through the faulty valve, resulting in the sound of a heart murmur (see handout “Mitral Valve Disease in Dogs”).  This is called mitral regurgitation.

"Mitral disease is most often diagnosed in small-breed dogs that are middle-aged to older."

As the valve leaks, the heart has to work harder to supply blood to the rest of the body. Over time, the heart can become stretched and enlarged from having to handle the extra blood flow caused by the regurgitation, and congestive heart failure can develop. Mitral disease is most often diagnosed in small-breed dogs that are middle-aged to older. Common breeds affected are Cavalier King Charles spaniel, dachshund, cocker spaniel, poodle, and chihuahua.

Dilated cardiomyopathy (DCM) is a disease in which the heart muscle degenerates and becomes thin and weak. As a result, the heart is unable to properly contract and pump blood, often leading to congestive heart failure (see handout “Dilated Cardiomyopathy in Dogs”). This disease is more commonly seen in larger breeds such as doberman pinschers, Portuguese water dogs, Irish wolfhounds, and Great Danes.

What are the signs of heart disease in dogs?

Most dogs display no clinical signs until the disease is advanced. Often, it may be detected when a veterinarian hears a heart murmur during a physical examination.

The most common signs of heart disease in dogs are:

  • coughing and difficulty breathing
  • exercise intolerance (easily tired on walks or when playing)
  • weakness and/or collapse
  • weight loss
  • lethargy
  • swelling or bloating of the abdomen (belly)stunted growth (puppies)

What types of congenital heart disease occur in dogs?

The most common types of congenital heart diseases in dogs are patent ductus arteriosus or PDA (see Handout “Patent Ductus Arteriosus in Dogs”), subaortic stenosis, pulmonary valve stenosis, and ventricular septal defect. Certain breeds can be more prone to these birth defects, such as bichon frise, poodle, pomeranian, keeshond, maltese, corgi, and yorkshire terriers.

"Most dogs show no symptoms and are often diagnosed when a veterinarian hears a heart murmur during a physical examination."

Most dogs show no symptoms and are often diagnosed when a veterinarian hears a heart murmur during a physical examination. The loudness of the murmur reflects the amount of turbulence but is not indicative of the severity of the disease.

Not all heart murmurs are associated with heart disease. Some may reflect another disease process such as anemia. Intermittent heart murmurs may occur in some normal dogs often when their heart rate is increased due to stress, and these physiologic murmurs have no impact on their health. Cardiac ultrasound (echocardiogram) is needed to diagnose a physiologic murmur.

How is heart disease diagnosed?

Depending on the murmur and the degree of clinical signs, further testing may be advised to determine the cause. The additional testing generally involves X-rays, electrical recording of the heart (ECG), and ultrasound examination (echocardiography). If your veterinarian suspects that the heart murmur is secondary to another disease, more extensive tests may be recommended.

How is heart disease treated?

The specific treatment will depend on the cause of the heart disease. Some congenital heart abnormalities in the dog, such as patent ductus arteriosus, can be surgically corrected. When a young puppy is diagnosed with heart disease, diagnostic testing will help determine the prognosis and whether medical treatment is necessary.

"It is essential that the instructions for your dog's heart medication are followed closely."

Adult-onset heart disease is often treated with medications to support heart function and treat abnormal heart rhythms. It is essential that the instructions for your dog's heart medication are followed closely. For drugs given more than once daily, doses should be spread out over the day as evenly as possible. Some heart medications can have serious adverse effects if stopped suddenly, so it is important that your dog receives the medication regularly and that prescription refills are requested ahead of time.

Your veterinarian will discuss specific drugs for your dog, if needed. Some commonly used medications for dogs include ACE inhibitors such as enalapril (Enacard®) or benazepril (Fortekor®); pimobendan (Vetmedin®); and diuretics such as furosemide or spironolactone. It is also important that your dog’s body weight be maintained in an optimal range, neither overweight nor underweight.

Your veterinarian may also recommend regular recheck examinations, laboratory testing, and imaging such as X-rays or echocardiograms. It is important to follow these recommendations to ensure the best management of your dog’s heart disease.

Prognosis can vary depending on when the heart disease is identified, what the condition is, and how effective treatment is. Many dogs diagnosed with mitral valve disease can live normal lives without progression to heart failure.

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