Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs, particularly affecting small breeds. Understanding the stages of disease and evidence-based management is essential for welfare-focused care.
MMVD causes progressive welfare compromise that accelerates dramatically once heart failure develops. In preclinical stages, dogs are typically unaffected. As the valve leaks more severely, dogs experience declining exercise tolerance, then episodes of acute respiratory distress from pulmonary oedema — which causes extreme distress as the dog struggles to breathe. Chronic low-grade symptoms including cough, reduced activity, and disrupted sleep accumulate over months. End-stage heart failure is characterised by severe breathlessness, anxiety, and distress. Early diagnosis, appropriate monitoring, and timely initiation of evidence-based treatment (pimobendan at Stage B2) substantially delays the onset of these welfare-significant symptoms. Owners must also learn to assess quality of life and have frank end-of-life conversations with their vets before crisis point.