AIMS: Atrial fibrillation (AF) is a common complication in patients with acute myocardial infarction and is associated with an increase in the risk of death. The excess mortality associated with AF complicating acute myocardial infarction has not been studied in detail. Observations indicate that AF facilitates induction of ventricular arrhythmias, which may increase the risk of sudden cardiovascular death (SCD). A close examination of the mode of death could potentially provide useful knowledge to guide further investigations and treatments. METHODS AND RESULTS: We analysed the relation between AF/atrial flutter (AFL) and modes of death in 5983 consecutive patients discharged alive after an acute myocardial infarction screened in the TRAndolapril Cardiac Evaluation registry. This cohort of patients with an enzyme-verified acute myocardial infarction was admitted to 27 centres in 1990-92. Survival status was obtained 2 years after screening of the last patient. An independent endpoint committee assessed the modes of death. Left ventricular ejection fraction was determined in all the screened patients and information about presence or absence of AF/AFL was prospectively collected. Sustained or paroxysmal AF/AFL was observed in 1149 patients (19%) during hospitalization. During follow-up, 1659 patients (34%) died: 482 (50%) patients with AF/AFL and 1177 (30%) patients without AF/AFL, P<0.001. SCD occurred in 536, non-SCD occurred in 725, and 398 died of non-cardiovascular causes (includes 142 unclassifiable cases). The adjusted risk ratio of AF/AFL for total mortality was 1.33 (95% CI: 1.19-1.49; P<0.0001) and the risk ratio for SCD was 1.31 (95% CI: 1.07-1.60; P<0.009). The adjusted risk ratio of AF/AFL for non-SCD was 1.43 (95% CI: 1.21-1.70; P<0.0001). CONCLUSION: The excess mortality observed in patients with AF/AFL following acute myocardial infarction is due to a significant increase in both SCD and non-SCD.