Does Your Dog Have Endocardiosis?
The most common heart disease in dogs, especially small breeds. Here's what endocardiosis means and how it's managed.
If your dog’s vet just mentioned a heart murmur, or you’ve noticed a cough that won’t quit and some reluctance to go on walks, you may have come across the word endocardiosis. Here’s what it actually means: the valves inside your dog’s heart, most often the mitral valve on the left side, slowly wear down with age. Instead of closing tight with each heartbeat, they get floppy and leaky, letting blood flow the wrong way. That backward leak strains the heart over time. It’s the most common heart disease in dogs, especially in small breeds, and it’s very manageable when caught and monitored early.
TL;DR
- Endocardiosis, also called mitral valve disease or MMVD, is age-related valve degeneration that causes blood to leak backward in the heart. It’s the most common heart disease in dogs, especially small breeds like Cavalier King Charles Spaniels.
- Signs range from a silent murmur with no symptoms in early stages to coughing, labored breathing, and exercise intolerance as the disease progresses toward congestive heart failure.
- Vets use a staging system (ACVIM stages B1 through D) to guide treatment. Early stages may need only monitoring; later stages are managed with medications like pimobendan and diuretics.
- Counting your dog’s resting respiratory rate at home is the best early warning sign of worsening heart failure and takes less than a minute.
- Cardiac care costs add up fast. Enrolling before a murmur or symptoms appear means future echocardiograms and medications are more likely to be covered.
What is endocardiosis in dogs?
Think of the mitral valve like a door between two chambers of the heart. In a healthy heart, that door closes completely with every beat, keeping blood moving in one direction. With endocardiosis, the valve flaps thicken, deform, and stop sealing properly. Blood leaks back through the gap, creating the whooshing sound your vet hears as a heart murmur. Over months or years, that constant backward pressure forces the heart to work harder, causing it to enlarge and eventually struggle to keep up.
It’s extremely common in older small-breed dogs. Cavalier King Charles Spaniels are especially prone, with most developing some degree of mitral valve disease by age 10. Other breeds frequently affected include Dachshunds, Poodles, Shih Tzus, and Chihuahuas. Larger breeds can develop it too, but it’s far less common.
What are the signs of endocardiosis, by stage?
The American College of Veterinary Internal Medicine (ACVIM) uses a four-stage system to classify how far the disease has progressed. Your vet will refer to these stages when making decisions about treatment.
Stage B1: A murmur, nothing else Your vet can hear a murmur, but the heart isn’t enlarged yet and your dog feels completely normal. Most owners don’t notice anything at this stage. No treatment is typically needed yet, just regular monitoring.
Stage B2: Murmur with an enlarged heart The heart has started to grow in response to the extra work. Your dog may still seem fine day-to-day, but this is when many vets will recommend starting pimobendan, a medication that helps the heart pump more efficiently and has been shown to delay the onset of heart failure.
Stage C: Congestive heart failure The heart can no longer compensate, and fluid starts to build up, usually in or around the lungs. This is when symptoms become obvious:
- A persistent cough, especially at night or after rest
- Faster or labored breathing, even while resting
- Exercise intolerance, tiring quickly on walks or reluctance to play
- Reduced appetite or weight loss
- Fainting or collapsing episodes
- A swollen belly, less common but possible
Stage D: Advanced, treatment-resistant heart failure The disease has progressed to a point where standard medication doses are no longer enough to control symptoms. Your vet may adjust or combine multiple medications to keep your dog comfortable. Quality of life becomes the central focus at this stage.
How do vets diagnose endocardiosis?
The process usually starts with a stethoscope. A murmur graded on a scale of 1 to 6 gives your vet an initial read on what’s happening. From there, diagnosis typically involves:
- Blood pressure and bloodwork: To rule out other contributing conditions and check organ health before starting medications.
- Chest X-rays: To check whether the heart has enlarged and whether there’s fluid in or around the lungs.
- Echocardiogram: The gold standard. A specialist uses sound waves to visualize the valve, measure how much blood is leaking, and assess heart chamber size and function. This is how your vet stages the disease and decides on treatment.
How is endocardiosis treated?
There’s no cure, but endocardiosis is very treatable, and many dogs live comfortably for years after diagnosis. Treatment is tailored to your dog’s specific stage:
- C and D: Pimobendan continues alongside diuretics to remove excess fluid from the lungs, and possibly additional medications to manage blood pressure and heart rhythm. Your vet may refer you to a veterinary cardiologist at this point.
- B1: Monitoring only. Regular vet rechecks and tracking symptoms at home.
- B2: Pimobendan is typically started here. Studies show it can delay the progression to heart failure by months.
How do you monitor your dog’s heart health at home?
Your dog’s resting respiratory rate is the single best early warning sign that fluid is building up in the lungs, and you don’t need any equipment to measure it.
How to count resting respiratory rate
Watch your dog’s chest rise and fall while they’re asleep or quietly resting. Count each rise as one breath and time it for 30 seconds. Multiply by two. That’s their rate. A normal resting respiratory rate for dogs is under 30 breaths per minute. If you’re consistently seeing numbers above 30, or if you notice a sudden jump of 5 or more breaths from your dog’s personal baseline, call your vet.
Track it consistently
Take the measurement at the same time each day, first thing in the morning works well. Keep a simple log, even a note in your phone. Over time, you’ll know what’s normal for your dog, which makes spotting a real change much easier. Several free apps are designed specifically for this, and some veterinary cardiology practices will ask you to use one.
Go to the ER if you see any of these
- Breathing rate over 40 at rest
- Open-mouth breathing or visible effort with every breath
- Blue or gray gums
- Fainting or sudden collapse
- Extreme restlessness and inability to get comfortable, especially at night
These are signs of a cardiac emergency. Don’t wait for a morning appointment.
Does pet insurance cover endocardiosis in dogs?
Yes, endocardiosis is eligible for coverage under a Lemonade Pet accident and illness policy, as long as the condition isn’t pre-existing. That means your dog shouldn’t be showing any signs or symptoms, including a heart murmur, before your policy starts or during your waiting period.
A single echocardiogram can run several hundred dollars, and medications like pimobendan are taken daily for the rest of your dog’s life. For Cavalier King Charles Spaniels and other small breeds prone to heart disease, getting coverage in place before any cardiac findings appear on the record is especially worth thinking about.
Before we go
Endocardiosis is a slow-moving disease for most dogs, and the outlook with good management is encouraging. Many dogs with stage B or early C disease maintain a good quality of life for years. Life expectancy varies depending on stage at diagnosis, breed, and how well the disease responds to treatment, so lean on your vet and cardiologist for a picture specific to your dog. Start tracking that resting respiratory rate tonight, and don’t skip the recheck appointments even when your dog seems fine. Those check-ins are how you stay ahead of the disease.
Frequently Asked Questions
What is the life expectancy of a dog with endocardiosis?
It varies significantly depending on the stage at diagnosis and how the dog responds to treatment. Dogs diagnosed at stage B1 or B2 can live for several more years with monitoring and medication. Stage C and D dogs have a more variable prognosis, and your veterinary cardiologist is the best person to give you a realistic timeline based on your dog’s specific case.
Is endocardiosis the same as a heart murmur?
Not exactly. A heart murmur is the sound the vet hears caused by blood leaking through a damaged valve. Endocardiosis (or mitral valve disease) is the underlying condition causing that leak. A murmur is one of the signs, not the disease itself.
At what age does endocardiosis typically develop in dogs?
Most dogs develop some degree of valve changes as they age, typically appearing in dogs over 5 years old and becoming more common after age 8. Cavalier King Charles Spaniels can develop it much earlier, sometimes before age 5.
Can endocardiosis in dogs be cured?
There is no cure, but it is manageable. The goal of treatment is to slow progression, reduce symptoms, and keep your dog comfortable and active for as long as possible. Many dogs respond well to medication and maintain a good quality of life for years.
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