QUEST Study (Häggström 2008): Pimobendan vs Benazepril in CHF from Canine MMVD

Bottom line

• The QUEST study (Häggström et al. 2008, J Vet Intern Med) is the landmark RCT demonstrating pimobendan's survival benefit in dogs with established CHF caused by naturally occurring MMVD: 260 dogs at 28 centers in Europe, Canada, and Australia were randomized to pimobendan or benazepril hydrochloride, both added to conventional therapy.¹
• Median time to the composite primary endpoint (sudden cardiac death, cardiac euthanasia, or treatment failure) was 267 days in the pimobendan group versus 140 days in the benazepril group — hazard ratio 0.688 (95% CI 0.516–0.916, P = .0099).¹
• The pimobendan benefit persisted after adjustment for all baseline variables, and being a Cavalier King Charles Spaniel, requiring a lower furosemide dose, and having a higher creatinine concentration were associated with longer time to the primary endpoint.¹
• QUEST established pimobendan as a superior choice to benazepril monotherapy in CHF from MMVD; combined with ACE inhibitor therapy, pimobendan now anchors Stage C and D MMVD management in ACVIM consensus.²
• This is a clinician-facing evidence summary. It is not a dosing protocol; confirm regimen, monitoring and contraindications against current product labeling and a veterinary formulary.

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What the evidence shows

Study design and population

QUEST was a prospective, single-blinded, multicenter trial with dogs randomized to pimobendan (0.4–0.6 mg/kg/d orally) or benazepril hydrochloride (0.25–1.0 mg/kg/d orally), both administered on a background of conventional therapy.¹ Two hundred and sixty client-owned dogs already in CHF attributable to MMVD were enrolled at 28 centers across Europe, Canada, and Australia. Eight dogs were excluded from analysis, leaving 124 randomized to pimobendan and 128 to benazepril for the primary analysis. The primary endpoint was a composite of cardiac death, cardiac euthanasia, or treatment failure.¹

Note on dosing: the dose ranges cited here are those used in the trial and reported verbatim in the published abstract. Prescribers must confirm current labeled dose instructions independently, as product labeling may differ.

Results and prognostic factors

One hundred and ninety dogs reached the primary endpoint. The median time to the primary endpoint was 267 days for pimobendan and 140 days for benazepril (overall median 188 days), with a hazard ratio of 0.688 (95% CI 0.516–0.916, P = .0099) favoring pimobendan.¹ The benefit of pimobendan persisted after adjusting for all baseline variables. The authors identified that a longer time to endpoint was also associated with being a Cavalier King Charles Spaniel, requiring a lower furosemide dose, and having a higher creatinine concentration, while increases in several indicators of cardiac enlargement (LA/Ao, vertebral heart scale, and percentage increase in left ventricular internal diameter in systole) were associated with a shorter time to endpoint, as was worse exercise tolerance.¹

The authors concluded: "Pimobendan plus conventional therapy prolongs time to sudden death, euthanasia for cardiac reasons, or treatment failure in dogs with CHF caused by MMVD compared with benazepril plus conventional therapy."¹

Context in current CHF management

The 2019 ACVIM consensus guidelines position pimobendan as a central agent for Stage C and D MMVD, with the QUEST data informing its superiority over ACE inhibitor monotherapy in established CHF.² Current practice typically combines pimobendan with a loop diuretic and an ACE inhibitor for Stage C dogs, rather than using any of these drugs as sole therapy. The QUEST study compared pimobendan against benazepril — it was not designed to test combination therapy — so additional studies inform the contemporary multi-drug regimen. The ACVIM guidelines note that management of MMVD has changed substantially, with new strategies for advanced heart failure.²

How this fits clinical practice

QUEST remains the foundational evidence source for pimobendan in CHF from MMVD. Its 28-center international design and pre-specified primary endpoint lend it high credibility, though it was not blinded (it was single-blinded) and directly compared pimobendan to benazepril rather than to placebo. In modern practice, most CHF dogs receive pimobendan plus a diuretic plus an ACE inhibitor; QUEST established that pimobendan outperforms ACE inhibitor monotherapy as the active comparator for symptomatic cases. The prognostic associations identified — lower furosemide requirement, Cavalier King Charles Spaniel breed, higher creatinine — provide useful clinical context for counseling owners. Confirm exact regimen and monitoring parameters against current product labeling and a veterinary formulary; do not infer specific doses from this summary.

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References

1. Häggström J, Boswood A, O'Grady M, et al. 2008. Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: the QUEST study. J Vet Intern Med 22(5):1124-1135. https://europepmc.org/article/MED/18638016
2. Keene BW, Atkins CE, Bonagura JD, et al. 2019. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. J Vet Intern Med 33(3):1127-1140. https://europepmc.org/article/MED/30974015 [via]

Changelog

• 2026-06-22: First published.