OBJECTIVE: To evaluate RBC distribution width (RDW) in dogs with chronic degenerative valvular disease (CDVD) with compensated or decompensated heart failure. DESIGN: Retrospective case-control study. ANIMALS: 27 healthy dogs and 135 dogs with CDVD (87 dogs with compensated heart failure and 48 dogs with decompensated heart failure). PROCEDURES: The RDW and various CBC and serum biochemical variables were compared among groups. Correlations between RDW and various echocardiographic variables were evaluated. RESULTS: Mean ± SD RDW in dogs with CDVD (13.1% ± 1.0%) was not significantly different from that of healthy dogs (12.8% ± 0.8%). The RDW of dogs with CDVD and compensated heart failure (13.0% ± 1.0%) was not significantly different from that of dogs with CDVD and decompensated heart failure (13.2% ± 1.1%). The RDW had a significant, weak, negative correlation with Hct (correlation coefficient, -0.250), hemoglobin concentration (correlation coefficient, -0.219), and mean corpuscular volume (correlation coefficient, -0.211). The RDW had a significant, weak, positive correlation with 1 echocardiographic index of CDVD severity (ie, the left atrium-to-aorta ratio [correlation coefficient, 0.183]). CONCLUSIONS AND CLINICAL RELEVANCE: In this study population, RDW did not seem to be associated with the presence of heart failure or CDVD.