Background: Atrial fibrillation is the most common sustained arrhythmia seen in clinical practice. It is responsible for increased mortality from all cardiovascular causes and shortens average life span. Aims: To know the various clinical presentations in atrial fibrillation and to detect various aetiological factors of atrial fibrillation.Methodology: This Observational study was conducted on 50 cases of atrial fibrillation.Cases were examined in detail as per proforma with special reference to cardiovascular system.Investigations like urine examination, complete Blood picture, Erythrocytes Sedimentation rate, Blood urea, Serum creatinine, Blood sugar, Serum electrolytes and chest X-ray examination have been carried out. Special investigations like electrocardiogram, echocardiogram was also done. Whenever necessary blood for culture and sensitivity, CT-Brain in case of stroke. The electrocardiogram was studied for rate and ‘f’ wave pattern. The echocardiogram was studied to assess the valvular lesion, Mitral Valve Area (MVA) in mitral stenosis cases, and enlargement of chambers particularly the left atrium size.Results: Most of the chronic atrial fibrillation is associated with large left atrial size, 4-5cms (56%).Congestive cardiac failure (60%), angina (32%), embolic stroke (14%) are common complications.Incidence of congestive cardiac failure, angina are high in patients of chronic AF with fast ventricular rate.Incidence of embolic stroke is more in rheumatic AF.Incidence of embolic stroke is high in non-rheumatic AF with the presence of risk factors like age >65yrs, HTN, DM, CCF, LA size > 4.5 cm.Most of the cases of AF associated with MVA is less than 1 sq.cm. (Severe) in RHD. Conclusion: Atrial fibrillation due to rheumatic aetiology is more common in younger age group, while the other causes like hypertension, ischemic heart disease common in older age.Females are commonly affected than males.Rheumatic heart disease is commonest cause followed by ischemic heart disease, Hypertension.