Myxomatous mitral valve disease in Labrador Retrievers and Golden Retrievers.

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To characterize myxomatous mitral valve disease (MMVD) in Labrador Retrievers (LRs) and Golden Retrievers (GRs). 52 LRs and 20 GRs diagnosed with MMVD composed a retrospective study sample (February 1, 2010, to July 31, 2021). Stored echocardiograms were remeasured. Dogs were staged by 2019 MMVD consensus guidelines. Mean age was 9.9 years in LRs and 9.5 years in GRs, with 31 of 52 LRs (59.6%) and 13 of 20 (65.0%) GRs being male. Forty-six LRs were stage B1 (88.5%), 3 were B2 (5.8%), and 3 were C (5.8%). Fourteen GRs were stage B1 (70.0%), 2 were B2 (10.0%), and 4 were C (20.0%). Of LRs and GRs in stage B2/C, 50% had systolic dysfunction. Atrial fibrillation (AF) and ventricular arrhythmias were identified in 2 of 52 (3.8%) and 10 of 52 (19.2%) LRs at initial diagnosis versus 3 of 20 (15.0%) and 3 of 20 (15.0%) GRs, respectively. All 5 AF dogs were stage C, with intermediate to high probability of pulmonary hypertension. Two additional GRs developed AF during follow-up; thus 5 of 6 (83.3%) stage B2/C GRs ultimately experienced AF. Subjective mitral valve thickening was frequent in both breeds (41/52 LRs [78.8%]; 18/20 GRs [90.0%]), while mitral valve prolapse was more common in LRs (22/52 [42.3%]) than GRs (5/20 [25.0%]). In LRs and GRs, MMVD was relatively late onset, with males overrepresented. Both breeds exhibited mitral valve thickening in association with MMVD, while LRs more commonly exhibited mitral valve prolapse. While most LRs and GRs with MMVD were stage B1, those in stage B2/C had increased prevalence of systolic dysfunction and AF.