Hello, wonderful pet parents! Today, we're going to talk about the most common heart disease in dogs, especially our small, senior friends: Myxomatous Mitral Valve Disease (MMVD). That's a mouthful, so we'll just call it Mitral Valve Disease. While it is a progressive disease, the great news is that with modern veterinary care, we can manage it for a long time and keep our beloved companions feeling great.
What is Mitral Valve Disease?
Your dog's heart has four chambers and four one-way valves that keep blood flowing in the right direction. The mitral valve is on the left side of the heart, between the left atrium (the top chamber) and the left ventricle (the main pumping chamber).
In Mitral Valve Disease, the valve leaflets become thick, lumpy, and distorted. This process is called "myxomatous degeneration." A thickened, lumpy valve can't close properly, so with each heartbeat, a little bit of blood leaks backward from the powerful left ventricle into the left atrium.
This backward leak is what causes the classic heart murmur associated with the disease. Over time, this leak can get worse, causing the left side of the heart to enlarge and eventually leading to congestive heart failure.
Who Gets Mitral Valve Disease?
This is primarily a disease of older, small to medium-sized dogs. The #1 breed affected is the Cavalier King Charles Spaniel, in which the disease is genetic and can appear at a much younger age.
Other commonly affected breeds include:
- •Dachshunds
- •Poodles (Miniature and Toy)
- •Chihuahuas
- •Shih Tzus
- •And many other small breeds and mixes
The Stages of Mitral Valve Disease
Veterinary cardiologists stage MMVD to help guide treatment. This staging system was created by the American College of Veterinary Internal Medicine (ACVIM).
- •Stage A: Dogs that are at high risk for the disease but have no signs yet (e.g., any Cavalier King Charles Spaniel).
- •Stage B1: Dogs that have a heart murmur, but the heart has not yet started to enlarge or change shape. No medication is needed at this stage, just monitoring.
- •Stage B2: Dogs that have a heart murmur AND their heart is enlarged (as seen on X-rays or an echocardiogram), but they do not yet have signs of heart failure. This is a key stage, as starting medication now can significantly delay the onset of heart failure.
- •Stage C: Dogs that have or have had signs of congestive heart failure (like coughing or difficulty breathing). These dogs require a cocktail of medications.
- •Stage D: Dogs with end-stage heart failure that is no longer responding well to standard treatment.
Spotting the Signs
Just like with DCM, in the early stages (B1 and B2), there are often no outward signs other than the heart murmur your vet hears.
As the disease progresses to Stage C, you will see signs of left-sided congestive heart failure:
- •Coughing: This is a huge one. It's often a soft, "wet" sounding cough that is worse at night, in the morning, or with excitement.
- •Increased Respiratory Rate: A resting breathing rate over 35 breaths per minute is a major red flag. You can learn to count this at home!
- •Difficulty Breathing (Dyspnea): This is an emergency.
- •Exercise Intolerance: Getting tired more easily on walks.
- •Fainting (Syncope): Can happen due to arrhythmias or poor blood flow.
How Vets Diagnose and Stage MMVD
- •Physical Exam: It all starts when your vet hears that classic left-sided heart murmur.
- •Chest X-rays: These are essential for seeing the size and shape of the heart and, most importantly, for checking for fluid in the lungs (pulmonary edema).
- •Echocardiogram (Heart Ultrasound): This is the gold standard test. An echo allows a cardiologist to see the thickened mitral valve, watch the blood leak backward, and take precise measurements of the heart's size and function. This is how Stage B1 is differentiated from Stage B2.
- •Blood Pressure: It's important to check for high blood pressure, which can make the leak worse.
Treatment: A Staged Approach
Treatment for MMVD is based on the stage of the disease.
- •Stage B1: No medication is needed. The recommendation is to have a recheck exam with your vet every 6-12 months.
- •Stage B2: The landmark EPIC study showed that starting the medication Pimobendan in this stage can delay the onset of heart failure by an average of 15 months! This is a huge deal and has changed how we treat this disease.
- •Stage C: Once a dog is in heart failure, a combination of medications is used. This almost always includes:
- •Pimobendan: To help the heart contract more strongly.
- •A Diuretic (like Furosemide): To get rid of the fluid in the lungs.
- •An ACE inhibitor (like Enalapril): To relax the blood vessels.
- •Sometimes, another diuretic called Spironolactone is added.
Prognosis
The prognosis for dogs with Mitral Valve Disease is highly variable, but many dogs can live for years with a good quality of life, even after being diagnosed with heart failure. The key is regular monitoring and sticking to the medication plan prescribed by your vet and veterinary cardiologist.
By catching the disease early and intervening at the right time, we can give our little companions many more happy years.
Sources & Further Reading:
- •ACVIM - Myxomatous Mitral Valve Disease (MMVD)
- 1VCA Animal Hospitals - Mitral Valve Disease in Dogs