Original Scientific Article Myxomatous mitral valve disease (MMVD) is one of the most common heart diseases in Cavalier King Charles spaniel (CKCS) dogs. The American College of Veterinary Internal Medicine (ACVIM) uses clinical, echocardiographic, and radiographic criteria to diagnose the disease, but measurement of vertebral left atrial size (VLAS) provides a simpler assessment. The aim of this study was to determine VLAS values in MMVD cases of CKCS and to investigate their clinical significance at different MMVD stages. Eighteen CKCS dogs of both sexes, different ages and weights, and different MMVD stages (6 at B1 stage, 6 at B2 stage, and 6 at C stage) were included in the study, as well as 6 healthy CKCS as control group A. We performed clinical, radiological, and echocardiographic examinations. VHS and VLAS values were significantly higher in the MMVD group than in the control group (p<0.001). VLAS showed high diagnostic accuracy in the detection of LA enlargement (area under the curve [AUC]: 0.98, cutoff ≥ 2.25, sensitivity: 88%, specificity: 100%, p<0.001). We also found high positive correlations between the VLAS and other values (LA /Ao, LVIDDn, and VHS) (r=0.88, r=0.88, and r=0.86, respectively) (p<0.001). It has been concluded that a VLAS value ≥2.25 can provide a meaningful diagnosis of left atrial enlargement in dogs with MMVD CKCS. https://macvetrev.mk/LoadArticlePdf/361 2023-7-19 165 170 https://doi.org/10.2478/macvetrev-2023-0023 left atrial size cavalier myxomatous mitral valve Gonul Remzi gonul@iuc.edu.tr false 1 Department of Internal Medicine, Faculty of Veterinary Medicine, Istanbul University Cerrahpasa, Avcılar Yerleşkesi, Üniversite Mahallesi, 34320 Avcılar/İstanbul, Türkiye LEAD_AUTHOR Hande Sağoğlu false 2 Department of Internal Medicine, Faculty of Veterinary Medicine, Istanbul University Cerrahpasa, Avcılar Yerleşkesi, Üniversite Mahallesi, 34320 Avcılar/İstanbul, Türkiye AUTHOR Murat Suzan false 3 Department of Internal Medicine, Faculty of Veterinary Medicine, Istanbul University Cerrahpasa, Avcılar Yerleşkesi, Üniversite Mahallesi, 34320 Avcılar/İstanbul, Türkiye AUTHOR Borgarelli, M., Haggström, J. (2010). 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