Abstract Funding Acknowledgements Type of funding sources: None. Introduction De novo atrial fibrillation (AF) is a frequent complication of acute coronary syndromes (ACS). However, 5-15% of patients (pts) admitted with suspected acute myocardial infarction have no significant lesions on coronary angiography (>50%) (MINOCA). Contrary to initial beliefs, MINOCA is not a benign disease, given that mortality and incidence of adverse events is similar to ACS. Objective To evaluate predictors and prognosis of AF in the setting of MINOCA. Methods Based on a multicenter retrospective study, data collected from admissions between 2013 and 2020. Pts without data on cardiovascular history or uncompleted clinical data were excluded. We included 7590 pts with non-ST elevation myocardial infarction (NSTEMI). Between those, 1561 (19.2%) were MINOCA. We divided MINOCA pts in 2 groups (G): GA – MINOCA with de novo AF; GB – MINOCA without de novo AF during in-hospital stay. Results MINOCA pts’ mean age was 65±13, 62% were male and 2.1% had de novo AF. GA pts were older (76±10 vs 65±13, p<0.001), had higher rates of Killip-Kimball class (KKC) >I (27.8% vs 9.7%, p=0.027) and kidney function impairment (50% vs 10.2%, p<0.001), lower haemoglobin at admission (13±1.5 vs 13.7±1.8, p=0.038), higher rates of diuretics (56.3% vs 17.6%, p<0.001) and amiodarone usage during hospitalization (31.3% vs 3.6%, p<0.001) and higher rates of left ventricle ejection fraction (LVEF)<50% (47.1% vs 19.1%, p=0.009). The Gs were similar regarding gender, times from symptoms to admission, cardiovascular risk factors and past history of heart failure, stroke or ACS, and heart rate and systolic arterial tension at admission. In the global population, older age (p=0.001, OR 1.87, CI 1.23-2.72), KKC>I (p=0.004, OR 1.76, CI 1.19-2.61) and LVEF<50% (p<0.001, OR 2.25, CI 1.5-3.38) were predictors of AF during hospitalization. In MINOCA pts, only older age (p=0.014, OR 4.2, CI 1.34-13.2) and LVEF<50% (p<0.001, OR 7.44, CI 2.17-25.47) were predictors of de novo AF. Regarding 1 year-prognosis, the occurrence of AF in MINOCA pts was associated with worse outcomes, namely 1year-mortality (log rank=0.002) and 1-year all cause readmission (log rank 0.028) Conclusion As expected, AF in the setting of MINOCA is associated with poorer prognosis. Pts with older age and LV dysfunction are at higher risk of de novo AF in this population.