Objective: of our study was to evaluate the incidence of acute fibrillation developing in the context of acute myocardial infarction population. Methodology: This cross-sectional study was carried out in department Cardiology Nishtar Hospital, Multan under supervision of senior cardiologists. Patients who were presented with acute myocardial infarction selected for study, duration April 2018 to February 2019. Data was entered and analyzed by using SPSS software, mean and SD representation was done for continuous data like age and frequency (percentages %) representation were done for categorical variables like gender, hypertension, DM, onset of old AF and new AF. chi square test was applied to see association between variables. P value less than or equal to 0.05 was considered as significant. Results: A total of 214 patients were enrolled in this study. There was association between new onset of AF and age (p=0.000). Old AF found in 7.9% (n=17) in patients. The main outcome of this study was new outset AF, in our study, it was found in 18.7% (n=40) patients. Conclusion: New onset of atrial fibrillation is a common type of Arrhythmia which is highly associated with ST segment elevation myocardial infarction or acute myocardial infarction. Keywords: Acute myocardial infarction, atrial fibrillation, prognosis, ST segment elevation.