Stage B1 MMVD in dogs: should you treat?
9-year-old asymptomatic Chihuahua with a grade 2/6 left apical systolic murmur. Echocardiography: myxomatous mitral valve degeneration with mild regurgitation, LA/Ao 1.3 and normalised left ventricular diastolic diameter (LVIDDN) 1.45. Radiographic VHS 10.2.
What is the recommended management?
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A. Start pimobendan to delay the onset of heart failure
The benefit of pimobendan (EPIC study) was shown only in dogs with cardiomegaly meeting stage B2 criteria. This dog does not: LA/Ao < 1.6 and LVIDDN < 1.7.
B. Start an ACE inhibitor (benazepril or enalapril) to slow progression
ACE inhibitors have not consistently been shown to delay progression in dogs with preclinical MMVD, let alone without cardiomegaly. The consensus does not recommend them in B1.
C. No treatment; reassess with echocardiography or radiographs every 6–12 months
Correct. In stage B1 (valvular lesion without enough remodelling to meet B2) no drug is recommended. The key is to monitor progression of cardiomegaly to detect the transition to B2.
D. Diet with severe sodium restriction and exercise restriction
Severe sodium restriction in preclinical stages may activate the renin-angiotensin-aldosterone system without proven benefit, and there is no need to limit normal exercise in an asymptomatic dog.
lightbulb Key takeaway
In B1 it is enough to avoid very salty foods and treats and keep normal physical activity. Small-breed dogs with louder murmurs (≥ 3/6) are more likely to have cardiomegaly and should be reassessed more often. Teach the owner to count the resting respiratory rate as a baseline.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.