AimsTailored heart failure treatment and risk assessment in patients following ST-segment elevation myocardial infarction (STEMI) is mainly based on the assessment of the left ventricular (LV) ejection fraction (EF). Assessment of the final infarct size in addition to the LVEF may improve the prognostic evaluation. To evaluate the prognostic importance of the final infarct size measured by cardiovascular magnetic resonance (CMR) in patients with STEMI.Methods and resultsIn an observational study the final infarct size was measured by late gadolinium enhancement CMR 3 months after initial admission in 309 patients with STEMI. The clinical endpoint was a composite of all-cause mortality and admission for heart failure. During the follow-up period of median 807 days (IQR: 669-1117) 35 events (5 non-cardiac deaths, 3 cardiac deaths, and 27 admissions for heart failure) were recorded. Patients with a final infarct size <median had significantly higher event rates than patients with a final infarct size <median (17 vs. 6; Log rank P 0.002). In a multivariable Cox regression analysis, including age, peak troponin T, LVEF, LV volume index, and heart rate, the final infarct size remained significantly associated with the occurrence of subsequent events (adjusted hazard ratio 1.13 per 1 increase (95 CI: 1.05-1.21; P 0.001). The overall Wald χ2 value of a model including known risk factors was 47.3, which increased to 57.9 when the final infarct size was added (P 0.001 for the difference).ConclusionAssessment of the final infarct size by CMR 3 months after a STEMI provides strong independent prognostic information incremental to known risk factors including the LVEF, and may help to improve the risk stratification of STEMI patients.