Boswood, AdrianGordon, Sonya G.Haggstrom, JensWess, G.Stepien, R. L.Oyama, Mark A.Keene, Bruce W.Bonagura, JohnMacDonald, Kristin A.Patteson, M.Smith, S.Fox, P. R.Sanderson, KarenWoolley, RichardSzatmari, ViktorMenaut, PierreChurch, Whitney M.O'Sullivan, M. LynneJaudon, J-PKresken, Jan-GerdRush, J.Barrett, K. A.Rosenthal, S. L.Saunders, Ashley B.Ljungvall, IngridDeinert, MichaelBomassi, EricEstrada, Amara H.Fernandez Del Palacio, Maria J.Moise, N. SydneyAbbott, Jonathan A.Fujii, YokoSpier, AlanLuethy, Michael W.Santilli, Roberto A.Uechi, MasamiTidholm, AnnaSchummer, ChristophWatson, P.2019-08-052019-08-052018-010891-6640http://hdl.handle.net/10919/92744Background: Changes in clinical variables associated with the administration of pimobendan to dogs with preclinical myxomatous mitral valve disease (MMVD) and cardiomegaly have not been described. Objectives: To investigate the effect of pimobendan on clinical variables and the relationship between a change in heart size and the time to congestive heart failure (CHF) or cardiac-related death (CRD) in dogs with MMVD and cardiomegaly. To determine whether pimobendan-treated dogs differ from dogs receiving placebo at onset of CHF. Animals: Three hundred and fifty-four dogs with MMVD and cardiomegaly. Materials and Methods: Prospective, blinded study with dogs randomized (ratio 1:1) to pimobendan (0.4-0.6 mg/kg/d) or placebo. Clinical, laboratory, and heart-size variables in both groups were measured and compared at different time points (day 35 and onset of CHF) and over the study duration. Relationships between short-term changes in echocardiographic variables and time to CHF or CRD were explored. Results: At day 35, heart size had reduced in the pimobendan group: median change in (D) LVIDDN -0.06 (IQR: -0.15 to +0.02), P < 0.0001, and LA: Ao -0.08 (IQR: -0.23 to +0.03), P < 0.0001. Reduction in heart size was associated with increased time to CHF or CRD. Hazard ratio for a 0.1 increase in DLVIDDN was 1.26, P - 0.0003. Hazard ratio for a 0.1 increase in DLA: Ao was 1.14, P = 0.0002. At onset of CHF, groups were similar. Conclusions and Clinical Importance: Pimobendan treatment reduces heart size. Reduced heart size is associated with improved outcome. At the onset of CHF, dogs treated with pimobendan were indistinguishable from those receiving placebo.application/pdfenCreative Commons Attribution-NonCommercial 4.0 InternationalCardiologyCardiovascularEchocardiographyEndocardiosisHeart FailureMitral regurgitationArticle - Refereedhttps://doi.org/10.1111/jvim.14885321292147231939-1676