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Myxomatous mitral valve disease (MMVD) is the most common acquired cardiac disease in dogs, accounting for approximately 70–75% of all canine heart disease. It is particularly prevalent in small- and medium-breed dogs, with increasing incidence and severity associated with advancing age. The disease is characterized by progressive degeneration of the mitral valve apparatus, resulting in mitral regurgitation, chronic volume overload, and ultimately, cardiac remodeling, increased filling pressures, and congestive heart failure (CHF).
Guideline-directed medical therapy for MMVD is based on disease stage, as defined by the American College of Veterinary Internal Medicine (ACVIM) consensus classification system. In dogs with preclinical disease and evidence of cardiac enlargement (Stage B2), pimobendan is recommended to delay the onset of CHF and prolong survival. Once CHF develops (Stage C), standard therapy includes a combination of pimobendan, loop diuretics, such as furosemide, and neurohormonal blockade with angiotensin-converting enzyme (ACE) inhibitors and spironolactone. These therapies target the central pathophysiologic mechanisms of heart failure, including impaired forward cardiac output, increased preload and afterload, and activation of the renin-angiotensin-aldosterone system (RAAS).
Pimobendan is a cornerstone of therapy due to its dual mechanism as an inodilator, providing both positive inotropy through calcium sensitization and balanced vasodilation through phosphodiesterase III inhibition. Clinical trials have demonstrated that pimobendan prolongs the preclinical period in dogs with Stage B2 MMVD and improves survival and quality of life in dogs with CHF. Current consensus guidelines recommend a labelled dose of approximately 0.4–0.6 mg/kg/day divided into two doses. However, despite appropriate guideline-directed therapy, MMVD is a progressive disease, and many dogs eventually develop worsening cardiac remodeling, recurrent congestion, increasing diuretic requirements, and progression to refractory heart failure (Stage D).
As disease advances, additional strategies beyond standard guideline recommendations are often pursued in clinical practice to optimize cardiac function and improve clinical stability.
One commonly utilized approach is dose escalation of pimobendan in dogs with progressive disease despite receiving the labelled dose. The typical initial escalation involves increasing the total daily dose by approximately 50%, to approximately 0.75–0.9 mg/kg/day divided twice daily, with further titration performed in select patients. Maximum total daily doses ranging from 1.5 to 3.0 mg/kg/day are used by some clinicians in advanced cases.
Clinical experience suggests that dose escalation may provide benefits, including improved forward cardiac output, reduction in cardiac chamber size, improved renal perfusion, decreased diuretic requirements, and reduction in syncopal events.
Beyond optimization of existing therapies, emerging treatments targeting complementary pathways involved in heart failure pathophysiology are gaining interest in veterinary cardiology.
Sodium-glucose cotransporter-2 (SGLT2) inhibitors, originally developed as antihyperglycemic agents, have demonstrated significant cardiovascular and renal benefits in human heart failure patients independent of diabetic status. These effects include improved myocardial energetics, reduction in preload and afterload, improved renal function, and attenuation of maladaptive neurohormonal activation.
Similarly, angiotensin receptor-neprilysin inhibitors (ARNIs), such as sacubitril/valsartan (Entresto®), provide dual modulation of the RAAS and natriuretic peptide systems, resulting in vasodilation, natriuresis, and inhibition of cardiac remodeling.
These therapies represent promising adjunctive options for dogs with advanced MMVD, particularly those with persistent congestion or progressive disease despite standard therapy.
