Mitral Valve Disease in Cavaliers: Screening, and What the EPIC Trial Found
Most Cavaliers develop a leaky heart valve. What the stages mean, why heart scans matter before symptoms, and what the EPIC trial and breeding schemes showed.
Written by thecanineledger
If your dog is breathing fast or hard at rest or asleep, coughing more than usual, has blue or grey gums, or collapses: see a vet now. These can be signs of heart failure.
In 2016, a trial in 360 dogs with a leaky mitral valve and an enlarged heart, but no symptoms yet, found that a heart medication delayed the onset of heart failure or cardiac death. The median time to that point was 1,228 days on the drug and 766 days on placebo. The authors called a delay of “approximately 15 months” a “substantial clinical benefit” (Boswood et al., Journal of Veterinary Internal Medicine 2016).
While that sounds like a reason to treat every dog with a murmur, it isn’t. The trial only included dogs whose hearts were already enlarged. This page explains what the disease is, what the stages mean, and why Cavalier owners should screen early.
1. What mitral valve disease is
The mitral valve sits between the two chambers on the left side of the heart. In myxomatous mitral valve disease (MMVD), it thickens and stops closing properly, so blood leaks backwards. A vet hears the leak as a murmur.
It is the commonest heart disease in dogs. The 2019 consensus guidelines from the American College of Veterinary Internal Medicine (ACVIM) say MMVD accounts for “approximately 75% of heart disease cases seen in dogs by veterinary practices” in North America (Keene et al., Journal of Veterinary Internal Medicine 2019).
Small dogs and age. “Prevalence is also higher in smaller (<20 kg) dogs”. In small breeds, the prevalence “increases markedly with age”, with “up to 85% showing evidence of the valve lesion by 13 years of age.”
Cavaliers. The guidelines name Cavalier King Charles Spaniels, Dachshunds, and Miniature and Toy Poodles as predisposed. They add that “the disease has an inherited component in some breeds”. A Swedish study of insured dogs under 10 found that Cavaliers had the second-highest death rate from heart disease of the 54 breeds it examined. Of 840 Cavaliers whose deaths were put down to heart disease, 309 (37%) had mitral valve disease recorded as the diagnosis (Egenvall et al., Journal of Veterinary Internal Medicine 2006).
Our note: A Danish study describes this 37% as a share of all deaths in Cavaliers under 10. The Swedish paper’s table shows it is a share of heart-related deaths only. The authors add that “The exact cardiac diagnosis for the claim was frequently not specified”. The study used insurance records from 1995 to 2002 and was supported by a pet insurer’s research foundation.
2. The stages
The ACVIM guidelines use four stages. Owners most often get lost between B1 and B2.
| Stage | What it means |
|---|---|
| A | At risk, no murmur yet. The guidelines’ example: “every Cavalier King Charles Spaniel or other predisposed breed without a heart murmur” |
| B1 | A murmur, no symptoms, and the heart is not enlarged enough to need treatment |
| B2 | A murmur, no symptoms, but the heart is enlarged enough “to recommend treatment before the onset of clinical signs” |
| C | Current or past signs of heart failure |
| D | Heart failure that no longer responds to standard treatment |
Why B1 and B2 matter. A murmur alone doesn’t tell your vet which stage your dog is in. That needs chest X-rays, a heart scan (echocardiogram), or both. The guidelines say B2 criteria “identify dogs that are likely to benefit substantially from treatment before the onset of clinical signs of heart failure.”
Stage B1 needs no drug. For B1, the guidelines say “No drug or dietary treatment is recommended”, and suggest a repeat heart scan “in 6‐12 months, depending on the imaging results”.
Our note: Stage D is our paraphrase of the guidelines’ “clinical signs of heart failure are refractory to standard treatment”. We don’t print the measurement thresholds for B2, so ask your vet to explain your dog’s scan report.
3. What the EPIC trial showed
The trial. EPIC enrolled 360 client-owned dogs with MMVD and an enlarged heart on X-ray and echocardiogram, and no signs of heart failure. Half received the trial drug and half a placebo.
The result. Dogs on the drug took a median of 1,228 days to develop heart failure or die of heart disease, against 766 days on placebo. The authors concluded that treatment “results in prolongation of preclinical period and is safe and well tolerated.”
Who paid. The trial’s conflict-of-interest declaration says it was funded by the drug’s manufacturer, and one author was an employee of the company.
Confirmed in primary care. A 2025 study using UK primary-care records tried to recreate the trial in ordinary practice. It concluded that it could “replicate results from an existing RCT in veterinary research, with similar treatment effects” (Pegram et al., PLoS One 2025). RCT is randomised controlled trial.
What it doesn’t show. The trial says nothing about dogs in Stage B1. Starting medication without a scan isn’t supported by it.
Our note: We don’t name the drug used at Stage B2. Your vet will tell you its name.
4. Screening Cavaliers
Yearly listening. The guidelines recommend that small, predisposed breeds “should undergo regular evaluations (yearly auscultation by the family veterinarian)”. Auscultation means listening with a stethoscope.
Breeding. The guidelines say “Potential breeding animals should no longer be bred if a murmur or echocardiographic evidence of mitral regurgitation (MR) is identified early, during the normal breeding age range”.
Breeding schemes work. In Denmark, a mandatory scheme for Cavaliers used listening and heart scans to decide which dogs could breed. After 8 to 10 years, dogs whose parents had both been approved had a “73% decreased risk” of a murmur compared with dogs examined at the start (Birkegård et al., Journal of Veterinary Internal Medicine 2016). Dogs with at least one unscreened parent showed no improvement.
If you are buying a Cavalier puppy. Ask whether both parents have been heart-screened, at what age, and by whom.
Our note: The puppy-buying advice is ours.
→ Choosing a Breed or a Mix: The Health Data Breeders Don’t Lead With
5. At home: counting sleeping breaths
Once your dog has a murmur, your vet may ask you to count its breathing rate while it sleeps. A rising rate can be the first sign of heart failure.
→ Heart Failure at Home: Counting Your Dog’s Sleeping Breaths
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “Every dog with a murmur needs medication” | No. The trial only included dogs with enlarged hearts (Stage B2). |
| “A murmur means heart failure” | No. A dog with a murmur and no signs is in Stage B. B1 dogs are rescanned, not medicated. |
| “You can tell the stage by listening” | Not reliably. Telling B1 from B2 needs X-rays or a heart scan. |
| “Breeding schemes don’t make a difference” | They can. A Danish scheme cut murmur risk by 73% over 8 to 10 years. |
| “The EPIC trial was independent” | No. The drug’s manufacturer funded it. A later primary-care study found similar effects. |
Sources
- Keene BW, Atkins CE, Bonagura JD, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med 2019: expert consensus
- Boswood A, Häggström J, Gordon SG, et al. The EPIC Study: A Randomized Clinical Trial in dogs with preclinical myxomatous mitral valve disease and cardiomegaly. J Vet Intern Med 2016: randomised controlled trial, 360 dogs. Title shortened here because it names the drug. Funded by the drug’s manufacturer
- Pegram C, Diaz-Ordaz K, Brodbelt DC, et al. Emulating the EPIC trial using VetCompass primary-care data. PLoS One 2025: target trial emulation, UK primary care
- Birkegård AC, Reimann MJ, Martinussen T, et al. Breeding Restrictions Decrease the Prevalence of Myxomatous Mitral Valve Disease in Cavalier King Charles Spaniels over an 8- to 10-Year Period. J Vet Intern Med 2016: Danish breeding scheme, 997 dogs
- Egenvall A, Bonnett BN, Häggström J. Heart disease as a cause of death in insured Swedish dogs younger than 10 years of age. J Vet Intern Med 2006: insurance records, 405,376 dogs, 1995 to 2002. Supported by a pet insurer’s research foundation. Read in full 5 November 2026
Always confirm with your vet before acting on anything on this page.