In humans, heart failure (HF) and renal insufficiency (RI) have negative reciprocal effects, and anemia can exacerbate their progression. In this retrospective study, the prevalence and prognostic significance of anemia in 114 dogs with degenerative mitral valve disease (DMVD) was investigated. Pretreatment clinical parameters, prevalence of anemia and azotemia, and survival time were analyzed in relation to HF severity. The prevalence of anemia was highest in dogs with the modified New York Heart Association (NYHA) class IV HF (33.3%), followed by classes III (15.2%) and II (0%; p < 0.001). The presence of anemia was associated with HF severity and blood creatinine > 1.6 mg/dL (both p < 0.001). Anemic dogs had a shorter median survival [13 months; 95% confidence interval (CI): 0.7–19.1] than nonanemic dogs (28 months; 95% CI: 15.3–40.7; p < .001). NYHA class IV (hazard ratio (HR): 3.1, 95% CI: 2.2–4.3; p < 0.001), left atrium/aorta ratio > 1.7 (HR: 2.7, 95% CI: 1.7–4.2; p = 0.001), and presence of anemia (HR: 1.43, 95% CI: 1.1–1.9; p = 0.004) emerged as predictors of mortality. A cardiorenal-anemia syndrome-like triangle was observed and anemia was a prognostic factor for survival in dogs with DMVD.