Background <p>Differentiating type 1 from type 2 non–ST-elevation myocardial infarction (NSTEMI) is clinically challenging, particularly in patients with atrial fibrillation (AF), where the 4th Universal Definition of Myocardial Infarction (UDMI) allows classification based on presumed mechanisms without mandatory coronary angiography. Real-world data from AF cohorts undergoing systematic invasive evaluation remain limited.</p> Methods <p>Between 2009 and 2020, we analyzed consecutive AF patients admitted with NSTEMI to a tertiary care center. Patients undergoing early coronary angiography were included. Infarct subtypes were adjudicated according to the 4th UDMI incorporating angiographic findings. The primary objective was to determine the prevalence of type 1 and type 2 NSTEMI. The secondary endpoint was a composite of all-cause mortality, myocardial infarction, stroke, or major bleeding.</p> Results <p>Among 536 eligible patients, 438 (81.7%) underwent coronary angiography. Of these, 312 (71.2%) were classified as type 1 NSTEMI, 100 (22.8%) as type 2 NSTEMI, and 26 (5.9%) as acute myocardial injury. Type 2 NSTEMI was associated with preserved left ventricular function and less extensive coronary artery disease. Over a median follow-up of 2.21&#xa0;years, composite event rates were 40.1% in type 1 and 36.0% in type 2 NSTEMI. Acute myocardial injury was associated with the highest composite event rate (65.4%) and all-cause mortality (57.7%).</p> Conclusions <p>In symptomatic AF patients, type 1 NSTEMI predominates and may be underdiagnosed without angiography, which enables accurate classification and timely revascularization. Type 1 and type 2 NSTEMI confer similarly high long-term risk, while acute myocardial injury identifies a particularly high-risk subgroup requiring systematic evaluation and targeted management.</p> Trial registration <p>Heidelberg Registry of Atrial Fibrillation [HERA‑FIB]; NCT05995561.</p> Graphical Abstract <p></p>