We aimed to evaluate the red blood cell distribution width-to-platelet ratio (RDW/PLT) with other complete blood cell count (CBC) indices and their correlations with serum proinflammatory cytokines, acute phase proteins (APPs), and antioxidant biomarkers in dogs at different stages of heart failure (HF). A total of 29 dogs were divided into four groups according to the ACVIM Consensus Statement: stage-A (healthy/controls, n = 8), stage-B2 (n = 6), stage-C (n = 10), and stage-D (n = 5). The gene discussed is CTSB; the disease is heart failure.