Cavalier Mitral Valve Disease (MVD) — Complete Guide to Symptoms, Stage-by-Stage Progression, and Heart Care

HeartBreed HealthMeongsiljang Veterinary Advisory Board

Cavalier King Charles Spaniels are a breed highly predisposed to mitral valve disease (MVD), with heart murmurs often beginning around age five and the condition progressing in most dogs by age ten. We’ve outlined the symptoms, diagnostic methods, and treatment options for each stage of the disease, along with key care tips for owners, such as daily respiratory rate monitoring.

What is Cavalier MVD? A Lifelong Condition Starting Around Age Five

A Cavalier King Charles Spaniel sitting calmly

Mitral valve disease (MVD) is a chronic heart condition common in Cavalier King Charles Spaniels, characterized by thickening and deformation of the mitral valve due to myxomatous degeneration, which leads to blood regurgitating into the left atrium (mitral regurgitation). Early detection and medication management according to ACVIM stages are crucial. As a breed highly predisposed to MVD, Cavaliers can be diagnosed at a young age (1–2 years), and the prevalence increases with age. In particular, nearly 100% of small-breed dogs over 10 years old show some degree of mitral valve degeneration. Therefore, it is important to monitor the disease stage through regular auscultation and echocardiography. When the disease progresses to stage B2, where cardiac enlargement is confirmed, starting pimobendan has been shown in the EPIC study to delay the onset of heart failure (or death from cardiac causes) by approximately 15 months.

Why Are Cavaliers Most Vulnerable to MVD?

Cavalier King Charles Spaniels are the breed most commonly affected by myxomatous mitral valve disease (MVD). The prevalence of MVD is high in small to medium-sized breeds, such as Cavaliers, Chihuahuas, Dachshunds, Miniature Poodles, and Miniature Pinschers, and it increases with age across all breeds. However, unlike other breeds, Cavaliers can be diagnosed at a young age, often between one and two years old. - Genetic predisposition: In Cavaliers, MVD is known to be a polygenic threshold trait, meaning multiple genes are involved. - Myxomatous degeneration: The collagen structure of the mitral valve undergoes myxomatous degeneration, causing the valve leaflets to thicken and prolapse. - Sexual dimorphism: Studies have reported that male dogs tend to develop the disease at an earlier age than females. The prevalence of MVD steadily increases with age, with reports indicating that nearly all small-breed dogs over the age of ten show some degree of mitral valve degeneration.

MVD Progression Stages — From A to D

Item	Heart murmur	Cardiac enlargement	Main symptoms	Treatment start
Stage A	None	Normal	None (at-risk breed)	Observation only
Stage B1	Present (mild to moderate)	Normal size	None	Regular follow-up
Stage B2	Moderate to severe	Enlargement begins	None (hard for owner to notice)	Start pimobendan
Stage C	Severe	Enlarged	Cough, dyspnea, exercise intolerance	Pimobendan + diuretics + ACE inhibitor
Stage D	Severe	Severe enlargement	No response to standard treatment	High-dose multi-drug combination

Based on the ACVIM 2019 consensus guidelines — the EPIC study found that starting pimobendan after a B2 diagnosis extends the time to onset of heart failure by about 15 months.

Seek Emergency Care Immediately, Even at Night, If You See These Signs

If you notice any of the following signs, seek emergency care immediately—even at night or on weekends. Pulmonary edema can become life-threatening within hours. - A resting respiratory rate of 40 breaths per minute or higher - Bluish or gray discoloration of the gums and tongue - Persistent dry coughing that continues even at rest - Sudden collapse or weakness in the hind legs - A respiratory rate more than double the normal baseline Save the location of a 24-hour emergency animal hospital in your phone in advance.

Daily Home Monitoring Checklist for Owners

Cavalier King Charles Spaniels show clear signs that owners can monitor at home. - Resting respiratory rate: Normal is fewer than 30 breaths per minute while sleeping or resting comfortably. - Exercise tolerance: They may stop frequently during their usual walks or pant for longer periods. - Nighttime coughing: Dry coughing may recur just before falling asleep or in the early morning hours. - Gum color: Pale, gray, or blue gums instead of pink indicate oxygen deficiency. Try making it a daily habit to place your hand on your dog’s chest before bed, count the breaths for 30 seconds, and multiply by two. Keeping a record of any changes will be very helpful during veterinary visits.

A pet owner checking the breathing rate of a Cavalier King Charles Spaniel

Diagnosis — The Three Pillars: Auscultation, Echocardiography, and Radiographs

Diagnosing MVD relies on three key pillars: auscultation, echocardiography, and thoracic radiographs. - Auscultation: A systolic murmur is typically the first sign, best heard at the left cardiac apex. - Echocardiography: We measure left atrial size (LA/Ao) and left ventricular dilation (LVIDDN) to distinguish between Stage B1 and Stage B2. - Thoracic Radiographs: The degree of cardiac enlargement is assessed using the Vertebral Heart Score (VHS) and Left Atrial Size (VLAS). The criteria for Stage B2 are an LA/Ao ratio of 1.6 or higher, an LVIDDN of 1.7 or higher, and a VHS exceeding 10.5. Pimobendan therapy is initiated only when these criteria are met.

Stage-by-Stage Treatment — Medications Are Added as the Disease Progresses

Treatment follows a stepwise approach, adding medications as the disease progresses. - Stage B2: Start with pimobendan alone — clinical trials (EPIC) showed it delayed the onset of heart failure by approximately 15 months. - Stage C: Combine pimobendan with furosemide (a diuretic) and an ACE inhibitor (such as enalapril). - Stage D: Add torsemide, spironolactone, and other agents to a high-dose, multi-drug regimen. Dosages are determined by your veterinarian based on your pet’s weight and kidney function. Do not adjust the dose or stop medication abruptly, as this can cause pulmonary edema to recur; always follow the prescribed regimen exactly.

A veterinarian listening to a Cavalier’s heart with a stethoscope

Daily Care for Cavaliers with Weak Hearts

Here are some daily care tips for Cavaliers with weak hearts. - Avoid walks between 12:00 PM and 4:00 PM during the peak of summer (rising body temperature increases cardiac burden). - Opt for short, frequent walks (we recommend two 15-minute walks instead of one 30-minute walk). - Consider low-sodium or cardiac-prescription diets (consultation with a veterinarian is essential). - Regular check-up intervals: every year when healthy, every 6 months from stage B1, and every 3 months from stage B2. - Always perform a cardiac evaluation before anesthesia or dental procedures. - Whenever possible, avoid environments that cause excitement or excessive barking, and use a lightweight X-shaped harness or chest strap instead of a harness that puts significant pressure on the chest.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

I was told my pet has a heart murmur. Should I start medication right away?

Not at all. For stage B1, there is no evidence that medication slows disease progression, so we simply monitor the patient regularly. Pimobendan is approved for use in stage B2, which involves cardiac enlargement, so we start it only after confirming stage B2 criteria—such as left atrial and left ventricular dilation—via echocardiography. We do not initiate medication based solely on the presence of a heart murmur detected during auscultation.

Do all Cavaliers develop MVD?

Almost all Cavaliers show some degree of mitral valve degeneration at some point in their lives. In fact, the prevalence increases with age, and it has been reported to reach nearly 100% in small-breed dogs over 10 years old. However, there is significant individual variation in the rate of progression and the timing of onset of heart failure. Since Cavaliers can be diagnosed at a younger age than other breeds, it is advisable to start regular check-ups early.

Are there any side effects of Pimobendan?

In the EPIC clinical trial, no significant difference in adverse event rates was reported between the pimobendan group and the placebo group, indicating that it is a relatively safe medication. However, as with any drug, individual responses can vary. Therefore, monitor your pet’s appetite, activity l

How far should I let my dog go on a walk?

Up to stage B1, you can continue your dog’s usual exercise routine. Starting at stage B2, take shorter, more frequent walks at an intensity that doesn’t cause excessive panting. From stage C onward, avoid heat, cold, and hills, and stick to short walks on flat ground. Recording how long it takes for your dog’s breathing to return to normal after each walk can help you monitor the progression of the condition.

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References

[1] Sharpe AN, Visser LC. Canine Myxomatous Mitral Valve Disease. In: Small Animal Critical Care Medicine, 3rd Ed.

[2] Stern JA, Walker AL. Pimobendan. In: Small Animal Critical Care Medicine, 3rd Ed.

[3] Ljungvall I, Häggström J. Myxomatous Valvular Disease. In: Textbook of Cardiovascular Medicine in Dogs and Cats.

[4] Keene BW et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med, 2019.

[5] Boswood A et al. Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study. J Vet Intern Med, 2016.