Mitral Valve Disease: The Most Common Heart Disease in Dogs

In an increasingly industrialised world where there’s been much talk about heart disease and its risks to human health, some might be surprised to hear that dogs can develop heart disease too – just in a completely different way. While coronary artery disease is common in people, mitral valve disease (MVD) is the most common heart disease in dogs. To understand MVD, it’s important to start with an understanding of heart anatomy.

The normal heart

The heart is divided into left and right sides. Each side is further divided into two chambers (an atrium and a ventricle) linked by a valve. The valve is termed the mitral valve on the left side, and the tricuspid valve on the right.
The heart pumps blood by contracting and relaxing. During this process, valves act as one-way doors – when the heart relaxes, the mitral and tricuspid valves open, allowing blood to flow from the atrium to the ventricle. When the heart contracts, the mitral and tricuspid valves close, preventing blood from flowing back into the atrium.

Simplified diagram of heart. White arrows represent flow of blood

What is MVD?

MVD develops when the mitral valve begins to lose function – imagine a one-way door that doesn’t close properly. When the heart contracts, some blood is pushed backward into the left atrium from the ventricle.
As a result, the next time the left ventricle contracts, it needs to work harder to push this additional blood on top of its usual workload.

Simplified diagram of contracted heart with MVD.

The valve loses function over time, resulting in the heart working progressively harder to sustain the increasing workload. This is a process that can be slowed, but not reversed.
Eventually, the heart may reach its limit. It still works to pump blood but cannot do so efficiently, and fluid builds up elsewhere in the body, particularly the lungs.
Any dog can develop MVD, but it occurs most commonly in elderly small-breed dogs. Example breeds include the Cavalier King Charles Spaniel, Shih Tzu, Toy and Miniature Poodles, Pomeranian and Miniature Schnauzer.

Symptoms of MVD

Dogs in early stages of MVD show no symptoms. They are termed to have heart disease.

If a dog progresses to the later stages of MVD, they begin to show symptoms. Once this occurs, they are termed to be in heart failure. This is a potentially life-threatening situation.

Below is a list of common heart failure symptoms. Those highlighted in red are emergencies and should be addressed immediately by a veterinarian.
- Lethargy
- Cough (typically soft and wet-sounding)
- Becoming tired more easily from exercise
- Breathing difficulties
- Collapse
- Blue-tinged tongue and/or gums

How is MVD diagnosed?

There are two common scenarios that can result in a diagnosis of MVD.

Scenario 1: Your dog is well. They are at the vet for a checkup or other minor issue. A vet listens to your dog’s chest and hears an abnormal heart sound (heart murmur – caused by backflow of blood). They suspect heart disease.

Scenario 2: Your dog is unwell. They present to the vet with the aforementioned emergency signs. A vet listens to your dog’s chest and hears a heart murmur. They suspect heart failure.

In either scenario, your vet may recommend chest X-rays and/or a specialised ultrasound scan of your dog’s heart (echocardiogram). The latter is the most accurate way to confirm the presence of MVD and differentiate it from other, less common diseases.

How is MVD treated?

Dogs not showing symptoms (i.e. with heart disease) are often first treated with Pimobendan. This improves the pumping function of the heart and slows progression of MVD.

If presenting as an emergency, dogs who show symptoms (i.e. in heart failure) may require hospitalisation before they are stable enough to continue treatment at home. On top of Pimobendan, furosemide and/or spironolactone are often added to relieve fluid buildup.

Some vets also prescribe benazepril to lower blood pressure and reduce the workload on the heart.
Because MVD cannot be reversed, affected dogs are often on medication for the rest of their lives. Your vet may therefore recommend:
- Regular rechecks
- Repeat echocardiograms
- Some form of at-home monitoring, such as counting the number of breaths your dog takes per minute while asleep.

The long-term outlook

Dogs diagnosed and treated before heart failure develops often live a few more years (bearing in mind they are often already elderly). Some never progress to heart failure and instead pass away from unrelated causes.
However, if heart failure develops, most affected dogs live less than 1.5 years after diagnosis.

Thank you for reading and we hope the information in this article has been useful for you and your pet. Please speak with your regular veterinarian if you have any specific concerns about your pet’s health.