OBJECTIVE: . Aim: The aim of this ambispective, two-center, observational study was to evaluate the clinical characteristics and 3-years prognosis of patients with non-STelevation myocardial infarction (NSTEMI) and AF. PATIENTS AND METHODS: Materials and methods: Patients hospitalized with a diagnosis of NSTEMI were included. Baseline demographic and clinical features, in-hospital procedures, and occurrence of cardiovascular events in patients with sinus rhythm (SR) and AF confirmed before admission were analyzed. RESULTS: Results: A total of 273 patients with NSTEMI were enrolled between 2012 and 2015, of whom 102 had AF (37.3%, 60.8% men) and 171 had SR (64.3% men). Patients with AF and NSTEMI were significantly older: 76.6±8.4 vs. 65.9±11.1 years (p<
0.0001). The permanent pattern of AF was observed in 54 patients (52.9%) and paroxysmal in 48 patients (47.1%). They more often had heart failure with higher NYHA class (p<
0.0001), type 2 diabetes (p=0.0001), abnormal renal function (p<
0.0001), and history of stroke (p<
0.0001). The presence of AF was not correlated with the number of stenotic coronary vessels. Significantly more NSTEMI patients with AF had a pacemaker implanted before admission (p<
0.0001). Duration of hospital stay of NSTEMI AF patients was longer: 10.5±9.9 vs.6.6±4.2 days and it was related to age, Rho=0.5,p=0.0002. During the 2-year and 3-year follow-ups, AF was significantly related to higher mortality, both cardiovascular disease and all-cause mortality (p<
0.0001). Independent long-term all-cause mortality predictors were heart failure, liver insufficiency, and age. At the 3-years follow-up, there were no significant differences in all-cause and cardiovascular mortality between groups with permanent AF and paroxysmal AF (p=0.696). CONCLUSION: Conclusions: Patients with atrial fibrillation and NSTEMI were older and more likely to have comorbidities. During the 2-year and 3-year follow-ups, AF was related significantly to higher mortality, both cardiovascular and of all causes. The long-term prognosis of patients with AF was adversely affected by heart failure, liver insufficiency and age.