The interval between the peak and end of the T-wave and the QT ratio (TpTe : QT) reflects the degree of repolarization heterogeneity in the myocardium and has high sensitivity for ventricular arrhythmia and mortality in humans. Based on this, the authors hypothesized that these markers are related to the myocardial pathological progression in canine dilated cardiomyopathy (DCM). The present report is a retrospective cohort study of Stage B2 DCM dogs diagnosed by experienced cardiology clinicians. Cases that died within two years after diagnosis were defined as the Early Mortality and all other cases were categorized as Controls. The TpTe : QT values were obtained by standard limb electrocardiogram and measured using the tangent method. The area under the curve (AUC) was used as the cutoff criteria for identifying the Early Mortality group. Out of 21 cases, 10 cases reached Early Mortality, while the remaining 11 cases were classified into the Control group. TpTe : QT showed a high AUC value with an optimal cutoff of 0.20 (sensitivity 89%, specificity 92%; AUC 0.90). In conclusion, TpTe : QT could be a potential prognostic indicator for Stage B2 DCM dogs. This study provided valuable information as a preliminary stage for a larger-scale clinical study to be conducted in the future.