Atrial fibrillation is the most common sustained arrhythmia and the incidence increases as the age advances. It can cause effort intolerance in those with left ventricular diastolic dysfunction due to loss of atrial booster function for ventricular filling. Thromboembolism is another risk associated with atrial fibrillation. Acute onset of atrial fibrillation is one of the important precipitating causes for heart failure in those with pre-existing heart disease. ECG shows a narrow QRS rhythm with absent P waves and totally varying RR interval with often more than 50% difference between the shortest and longest. Fibrillary waves are seen as fine undulations of the baseline. When the atria are enlarged, coarse fibrillary waves are seen. Most often, atrial fibrillation is treated with drugs which slow the AV nodal conduction like digoxin, beta blockers or verapamil. These drugs have to be used with caution in the elderly when the possibility of atrial fibrillation being part of a tachy-brady syndrome is high. Anti-coagulation is needed to prevent thromboembolism in those at risk. When atrial fibrillation is associated with hemodynamic compromise in the form of hypotension, angina or heart failure, cardioversion may be needed. When elective cardioversion is being planned for atrial fibrillation which has lasted more than 48 hours, the risk of thromboembolism has to be considered. Anticoagulation for 3 weeks prior to cardioversion is conventionally practised. Exclusion of intracardiac thrombi, specifically left atrial appendage clot, by a trans-esophageal echo followed by cardioversion is another strategy, especially when it is needed in a semi-urgent situation.