OBJECTIVE To investigate the determinants and the prognostic value of fragmented QRS (fQRS) after AMI. METHODS Prospective cohort of 307 consecutive patients with AMI. METHODS MACE (death plus non-fatal recurrent MI), hospitalization for an episode of heart failure, ventricular arrhythmia (VT or VF) at two years follow-up. RESULTS On the serial 12-lead ECG recorded during the in-hospital stay, 162 (53%) had no fQRS (no fQRS group). 145 (47%) presented an fQRS, which was persistent in 108 (34%) patients (persistent fQRS group) and transient in 37 (12%) patients (transient fQRS group). Patients with a fragmented QRS (transient or persistent) were older, more likely to be hypertensive and less likely to be smokers than were patients without fQRS. By multivariate logistic regression analysis, only hypertension (OR (95% CI): 1.66 (1.00-2.74); p = 0.047) was associated with an fQRS. During a mean follow-up of 846 ± 297 days, there were 82 MACE recorded: 17 patients died from a CV cause (10% event rate) among patients without fQRS, 22 (20% event rate) among patients with persistent fQRS and 3 (8% event rate) among patients with transient fQRS. Similarly, non-fatal recurrent MI occurred more frequently in patients with fQRS (18 (16%) and 10 (27%)) for persistent and transient fQRS, respectively, vs. 16 (10%) in the no fQRS group (p = 0.019). However, the occurrence of heart failure symptoms and ventricular arrhythmia was not significantly different (p = 0.162 and p = 0.242, respectively). Survival analysis by the Kaplan-Meier method showed a significant difference (log rank p = 0.026) between groups, and only persistent fQRS was associated with decreased survival. In multivariate cox regression analysis, the GRACE score, blood glucose on admission, and B-blockers in the acute phase were independent predictors of MACE at two years. fQRS was not a significant independent predictor of MACE (HR (95% CI): 1.57 (0.95-2.60); p = 0.08). Moreover, fQRS was not a predictor of heart failure or ventricular arrhythmia in univariate analysis. CONCLUSIONS Persistent fQRS on a 12-lead ECG is a marker of decreased survival after AMI, whereas transient fQRS correlates with recurrent MI.