When the duration of an episode of AF/AFL is uncertain, we suggest that patients may undergo cardioversion guided by transesophageal echocardiography, as an alternative to anticoagulation prior to cardioversion. However, anticoagulation needs to be simultaneously started and maintained for &ge;4 weeks postcardioversion. (Recommendation Conditional, Quality High)<br /><br /><b>Values and preferences: </b> This recommendation places a higher value on the symptomatic improvement with immediate cardioversion as well as avoidance of precardioversion anticoagulation. A lower value is placed on the small risks associated with transesophageal echocardiography.