We report the time to stable ST-segment reperfusion (TSTR) after primary angioplasty and its relationship with the clinical results; 137 patients who underwent primary angioplasty were included as part of the analysis. All patients had 24 hours ST-segment monitoring. Time to stable STR was defined as the beginning of ST-segment reperfusion (STR) lasting >4 hours without ST-segment reelevation. Six-month mortality was associated with slower TSTR (median 166.5 vs 6 minute, P = .001). Time to stable STR cutoff value of 136.5 minutes was identified as the best mortality predictor (area under the curve: 0.86, P = .001). Multivariate analysis identified Killip class > or = 2 (P = .042), TSTR cutoff value (P = .002), and final thrombolysis myocardial infarction (TIMI) flow grade III (P = .067) as predictors of 6-month mortality. Time to stable STR may be a novel continuous electrocardiogram (ECG) parameter following primary angioplasty, which can identify high-risk patients that need to be considered for additional treatments.