The aim of the present study was to clarify the prognostic significance of upright T waves (amplitude > 0 mV) in lead aVR in patients with a prior myocardial infarction (MI). We retrospectively examined 167 patients with a prior MI. The primary end point was cardiac death or hospitalization for heart failure. During a follow-up period of 6.5 ± 2.8 years, 34 patients developed the primary end point. A Kaplan–Meier analysis showed a lower primary event-free rate in patients with upright T waves in lead aVR than in those with nonupright T waves in lead aVR (P = 0.001). Univariate Cox proportional hazards regression analyses showed that age, gender, chronic kidney disease, anterior wall MI, upright T waves in lead aVR, left ventricular ejection fraction, loop diuretic use, and spironolactone use were significantly associated with the primary end point. A multivariate Cox proportional hazards regression analysis selected age [hazard ratio (HR) 1.10, 95% confidence interval (CI) 1.05–1.16, P < 0.001], upright T waves in lead aVR (HR 3.10, 95% CI 1.23–7.82, P = 0.017), and loop diuretic use (HR 4.61, 95% CI 1.55–13.67, P = 0.006) as independent predictors of the primary end point. In conclusion, the presence of upright T waves in lead aVR is an independent predictor of cardiac death or hospitalization for heart failure in patients with a prior MI. The analysis of T-wave amplitude in lead aVR provides useful prognostic information in patients with a prior MI.