Mitral Valve Disease in Dogs: What Every GP Vet Should Be Able to See on Echo
- Echo Vet Solutions
- Jul 1
- 8 min read
Myxomatous mitral valve disease (MMVD) is the most common acquired cardiac condition in dogs. It accounts for the majority of heart disease seen in first-opinion practice, and the decisions that follow its detection — when to image, how to stage, when to start treatment — fall squarely on the shoulders of the GP vet.
Echocardiography is the gold standard for staging MMVD. And yet many general practitioners feel uncertain around the echo examination, either because they have had limited hands-on training, or because they are unsure what findings they are actually looking for once the probe is in their hand.
This post is written for those vets. It covers the core echocardiographic findings in MMVD, the measurements that drive staging and treatment decisions, and the practical skills that make the difference between a scan that is merely performed and one that genuinely informs clinical management.
Why MMVD Matters More Than Ever for GP Vets
MMVD is not a condition that can be reliably managed from auscultation and radiographs alone. The 2019 ACVIM Consensus Guidelines on MMVD updated the criteria for staging and treatment in a way that places echocardiography at the centre of decision-making for preclinical disease.
The landmark EPIC study (Boswood et al., 2016) — a prospective, randomised, placebo-controlled trial involving 360 dogs across multiple international centres — demonstrated that administering pimobendan to preclinical (Stage B2) dogs with echocardiographic and radiographic evidence of cardiomegaly delayed the onset of congestive heart failure by approximately 15 months. That is a substantial clinical benefit, and it depends entirely on accurate identification of Stage B2 disease — which in turn depends on reliable echocardiographic measurement.
Without echo, you cannot stage with confidence. Without staging, you cannot treat appropriately. The consequences of missing B2 disease are real and measurable in patient outcomes.
A Brief Guide to the ACVIM Staging System
Understanding what you are looking for on echo requires familiarity with the staging framework. The ACVIM classifies MMVD into the following stages:
Stage A — Breeds at high risk of MMVD (e.g. Cavalier King Charles Spaniels, Dachshunds, Miniature Poodles) with no currently detectable disease.
Stage B1 — A heart murmur consistent with mitral regurgitation, but without sufficient cardiac remodelling to meet B2 criteria. No treatment is currently recommended at this stage.
Stage B2 — A heart murmur plus echocardiographic evidence of cardiac enlargement meeting all three of the following criteria: LA:Ao ≥ 1.6, LVIDdN ≥ 1.7, and VHS > 10.5. This is the critical intervention point — pimobendan is recommended.
Stage C — Current or historical signs of congestive heart failure (CHF), typically cardiogenic pulmonary oedema. Active medical management is required.
Stage D — Refractory CHF despite optimised standard therapy. Requires specialist input.
For GP vets, the most clinically significant distinction is between B1 and B2, because this is where the treatment decision is made. And that distinction hinges on two echocardiographic measurements.
The Two Measurements That Matter Most
LA:Ao — Left Atrial to Aortic Root Ratio
The LA:Ao ratio is measured from the right parasternal short-axis view at the level of the aortic valve, in early diastole (immediately after the aortic valve closes). It compares the diameter of the left atrium to the diameter of the aortic root.
Normal value: < 1.6 B2 threshold: ≥ 1.6
Left atrial enlargement is the most sensitive indicator of volume overload secondary to mitral regurgitation. A dilated left atrium reflects the chronic pressure and volume changes upstream of the incompetent valve. It is often the first chamber to enlarge in MMVD, and its measurement is your most important single data point.
Practical tips for measuring LA:Ao:
Use the right parasternal short-axis view — do not attempt this measurement from a left-sided window
Freeze the image in early diastole, immediately as the aortic valve leaflets come together
Measure the internal dimensions of the left atrium and the aortic root at the same level — the leading edge to leading edge method is standard
Avoid measuring mid-systole, when the aortic root is at its smallest and the ratio will be artificially elevated
LVIDdN — Left Ventricular Internal Diameter in Diastole, Normalised for Body Weight
The LVIDdN is an M-mode measurement taken from the right parasternal long- or short-axis view at the level of the chordae tendineae, at the point of maximum left ventricular dimension (end-diastole). The raw LVIDd measurement is then normalised for body weight using the formula:
LVIDdN = LVIDd (cm) ÷ body weight (kg)⁰·²⁹⁴
Normal value: < 1.7 B2 threshold: ≥ 1.7
Left ventricular enlargement reflects the increased stroke volume the heart must generate to maintain forward flow in the face of regurgitation. An LVIDdN ≥ 1.7 tells you the ventricle has remodelled to a degree that warrants intervention.
Practical tips for measuring LVIDdN:
Use M-mode cursor positioned perpendicular to the interventricular septum and free wall, at the level of the chordae — not through the papillary muscles
Measure at the widest point (end-diastole), from the endocardial surface of the septum to the endocardial surface of the free wall
Always note the patient's body weight before scanning — you cannot calculate LVIDdN without it
What the Mitral Valve Itself Should Look Like
Before you focus entirely on chamber measurements, it is worth spending time assessing the valve itself. The echocardiographic appearance of the mitral valve in MMVD follows a recognisable pattern:
-Leaflet thickening and nodularity. The anterior and/or posterior mitral valve leaflets become irregular and hyperechoic compared to normal. Early disease may show subtle nodular thickening at the leaflet tips; more advanced disease produces pronounced, lumpy leaflet margins visible in both long- and short-axis views.
-Prolapse. Mitral valve prolapse (MVP) — where one or both leaflets bow back beyond the mitral annular plane into the left atrium during systole — is characteristic of MMVD. It is best assessed from the right parasternal long-axis four-chamber view and the left apical four-chamber view. Note that mild MVP in certain breeds (particularly CKCSs) can be a normal variant at low grades.
-Mitral regurgitation jet on colour Doppler. Colour flow Doppler imaging will reveal the regurgitant jet originating from the mitral valve and directed into the left atrium during systole. The presence, direction, and size of the jet give important qualitative information about regurgitation severity. Central jets are more typical of symmetric disease; eccentric jets suggest leaflet prolapse or flail. A detailed quantitative assessment of jet severity is beyond first-opinion scope, but recognising the presence and rough magnitude of regurgitation is achievable with basic training.
Practical Scanning Tips Specific to Cardiac Echo
For vets who already perform abdominal ultrasound, transitioning to echocardiography requires some adjustments in approach:
Patient positioning. Cardiac echo in dogs is performed in lateral recumbency, ideally on a purpose-designed echocardiography table with a cut-out to allow the probe to be directed upward through the table. This right lateral position gives access to the right parasternal windows without the probe competing with the examination table for space. If a cut-out table is unavailable, positioning at the edge of a standard table is a workable alternative, though more physically demanding.
Probe selection. A microconvex or phased array transducer is preferred for echocardiography. The phased array probe, with its very small footprint and sector beam, is specifically designed for cardiac work and provides excellent image quality in the intercostal spaces where the probe must fit between ribs.
Heart rate. Dogs undergoing echocardiography are often anxious, resulting in elevated heart rates that compress the cardiac cycle and make measurement more challenging. Minimise restraint stress where possible and, if needed, allow a brief settling period before taking measurements. In tachycardic patients, freeze during a run of more regular beats and measure from consistent phases of the cardiac cycle.
Freeze and measure. Many GP vets are accustomed to reviewing clips in real-time during abdominal scanning. Accurate echocardiographic measurement requires a disciplined approach to freezing, scrolling frame by frame, and measuring at precisely the correct point in the cardiac cycle. This is a skill that improves rapidly with supervised practice.
When to Refer — and When Not To
Developing a basic echo capability for MMVD staging does not mean managing all cases in-house. The aim for first-opinion practice is to make reliable measurements that allow you to distinguish B1 from B2, make treatment decisions in straightforward cases, and identify patients who need specialist input.
Refer when:
Findings are atypical or unexpected for MMVD (e.g. suspected DCM, structural anomaly, pericardial effusion)
Systolic function appears reduced
The dog is in or approaching heart failure and you need a full haemodynamic assessment
Measurements are borderline and the treatment decision is genuinely uncertain
The owner is asking questions that go beyond the scope of your current training
Manage in practice when:
Measurements clearly satisfy B2 criteria and the murmur history is consistent
The dog is stable B1 and requires monitoring at 6–12-month intervals
You are confident in your measurement quality
Knowing the limits of your current skill level — and working actively to extend them — is what separates good from great clinical practice.
The Skills Gap in General Practice
A survey of GP vets in Dutch-speaking Western European countries found that while 60% reported using the ACVIM guidelines for MMVD staging, 40% did not — with over half of that group citing difficulty identifying the stages as their primary reason. A separate study validated that focused echocardiographic training in first-opinion practice leads to clinically meaningful agreement between trained GPs and cardiology diplomates in staging MMVD and determining pimobendan eligibility.
These findings point clearly to a skills gap that is addressable. The echo measurements required to stage MMVD are not complex — but they require structured, hands-on training to perform reliably and confidently.
Want to Be Confident Staging MMVD in Your Own Practice?
At Echo Vet Solutions, our in-practice echocardiography training is designed precisely for this scenario: GP vets who are confident with auscultation and radiographs, but want to add reliable echocardiographic assessment to their cardiac toolkit.
Our training is entirely hands-on, delivered at your practice, on your own patients, with your own equipment. We don't run lecture-based CPD events. We come to you, and we work through real cases together — including measurement of LA:Ao, LVIDdN, Doppler assessment of mitral regurgitation, and systematic evaluation of the cardiac chambers.
Our instructors hold advanced qualifications and have extensive experience teaching echocardiography.
References and Further Reading
Boswood A et al. (2016). Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study. Journal of Veterinary Internal Medicine, 30(6):1765–1779. PubMed
Keene BW et al. (2019). ACVIM Consensus Guidelines for the Diagnosis and Treatment of Myxomatous Mitral Valve Disease in Dogs. Journal of Veterinary Internal Medicine, 33(3):1127–1140. Wiley Online Library
Hezzell MJ et al. (2022). Validation of a focused echocardiographic training program in first opinion practice. Journal of Veterinary Internal Medicine, 36(6):1913–1922. Oxford Academic
Tauber G et al. (2023). Self-Reported Utilization of International Guidelines for Staging Dogs with Myxomatous Mitral Valve Degeneration. PMC. Read article
Vettimes (2024). Diagnosis and management of mitral valve disease in dogs. Read article
Häggström J et al. (2008). Effect of pimobendan or benazepril hydrochloride on survival times in dogs with CHF due to MMVD: the QUEST Study. Journal of Veterinary Internal Medicine, 22(5):1124–1135 .
Wilshaw J, Rosenthal SL, Wess G, Dickson D, Bevilacqua L, Dutton E, Deinert M, Abrantes R, Schneider I, Oyama MA, Gordon SG, Elliott J, Xia D, Boswood A. Accuracy of history, physical examination, cardiac biomarkers, and biochemical variables in identifying dogs with stage B2 degenerative mitral valve disease. J Vet Intern Med. 2021 Mar;35(2):755-770. doi: 10.1111/jvim.16083. Epub 2021 Mar 1. PMID: 33645846; PMCID: PMC7995403. Read article.
Echo Vet Solutions delivers bespoke in-practice echocardiography and ultrasound training across the UK. Our instructors hold advanced clinical qualifications in small animal cardiology. To find out how we can help your practice manage MMVD with greater confidence, visit echovetsolutions.co.uk.
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