Mitral Valve Disease (MVD)

Mitral valve disease is the most common acquired heart condition in dogs, accounting for approximately 75% of all cardiac disease cases. The mitral valve, which separates the left atrium from the left ventricle, develops nodular thickening and degenerates over time - the valve leaflets fail to close properly, causing blood to flow backwards (regurgitation) from the left ventricle into the left atrium with each heartbeat.

This creates a heart murmur (the sound of turbulent regurgitant flow) and gradually reduces cardiac output. Over time, the heart compensates by enlarging, until eventually it can no longer compensate - and congestive heart failure develops.

MVD is particularly prevalent in small and toy breeds. Cavalier King Charles Spaniels are affected earlier and more severely than any other breed, with most developing MVD by age ten and some developing it as early as two to three years.

Progression

MVD follows a predictable natural history:

• Stage B1: Heart murmur present; no cardiac enlargement; no symptoms
• Stage B2: Heart murmur present; left atrium and ventricle enlarged (on X-ray or echocardiogram); no symptoms - this is the stage where medication (pimobendan) is now recommended before symptoms develop
• Stage C: Congestive heart failure - active or recently treated
• Stage D: Refractory heart failure - not adequately controlled with standard therapy

Resting respiratory rate - your key home monitoring tool

For dogs with known MVD (any stage), measure and log the resting respiratory rate (RRR) daily:

• Count breaths (one in-out = one breath) while the dog is sleeping
• Normal sleeping RRR: below 30 breaths per minute
• Log the reading and time

Establish your dog's personal baseline over the first few weeks of monitoring. An RRR that rises above 30, or that increases significantly above the personal baseline, is the earliest detectable home indicator of developing congestive heart failure.

A consistent RRR above 30 - or any sudden rise - contact your vet the same day.

Other signs to monitor weekly

• Cough. A soft, nocturnal cough - particularly at rest or during the night - may indicate early pulmonary oedema (fluid in the lungs). Note frequency, time of day, and character.
• Exercise tolerance. Compare to a previous baseline. A dog who previously walked a mile now struggles at half a mile.
• Appetite. Reduced appetite, particularly if persistent, suggests worsening cardiac status.
• Abdominal distension. Ascites (fluid accumulation in the abdomen) can accompany right-sided heart failure.
• Fainting (syncope). Sudden collapse during or after exercise or excitement requires same-day assessment.

Treatment milestones

Murmur detection (Stage B1): No medication required. Begin RRR monitoring. Schedule 12-monthly cardiac assessments including echocardiography.

Cardiac enlargement detected (Stage B2): Pimobendan (Vetmedin) is now standard of care - it delays onset of heart failure in dogs meeting Stage B2 criteria. This is a significant development in MVD management.

Heart failure (Stage C/D): Typically managed with pimobendan, furosemide (or torasemide), and an ACE inhibitor. Dose adjustments are guided by clinical response and RRR monitoring.

When to contact your vet

Go to the emergency vet if:

• Breathing is clearly laboured or distressed
• Your dog cannot settle and is clearly struggling to breathe
• RRR is above 40 or the dog appears to be gasping
• Collapse

Contact your vet the same day if:

• RRR has risen consistently above 30 over several days
• A new cough has developed
• Your dog seems suddenly much less able to exercise

Schedule routine monitoring for:

• Annual echocardiography for Stage B1 dogs
• More frequent monitoring for Stage B2+ dogs per your vet's schedule

Frequently Asked Questions

My vet detected a heart murmur in my young Cavalier - how serious is this? Murmurs in young CKCSs warrant echocardiography to assess whether structural MVD is present. The Cavalier Health's MVD Breeding Scheme recommends annual cardiac assessments. Detecting Stage B1 early establishes a monitoring baseline and catches the transition to B2 (when treatment is recommended) promptly.

Can MVD be cured? Not medically, and surgical valve repair in dogs is available only at a small number of specialist centres and carries significant cost and risk. For most dogs, MVD is managed with medication to delay and control heart failure.

My dog is on three heart medications - is that normal? Yes. Heart failure management typically involves multiple medications acting at different points: pimobendan to improve heart muscle function, a diuretic to clear fluid, and an ACE inhibitor to reduce cardiac workload. More advanced cases may add further medications.

How accurate is my home RRR measurement? Reasonably accurate if done consistently. Count for 30 seconds and multiply by two; take readings when the dog is in deep sleep (slow, regular breathing) rather than dreaming (irregular). Your personal baseline is what matters - compare today's reading to your established normal.

What happens when heart failure develops despite treatment? Stage C management aims to return the dog to clinical comfort and resume normal activity. Many dogs with heart failure are well-managed for months to years on appropriate medication. When Stage D (refractory failure) develops, the focus shifts to quality of life assessment and palliative care. Regular vet review is important throughout.