From the time of its introduction as a clinical tool in the early 1970s, efforts have been made to use echocardiography to characterize the atrium and its function as these relate to attempted cardioversion and embolic risk. M-mode and 2-D echo studies suggest left atrial size is not a definitive determinant of the potential for successful cardioversion. Doppler studies show that atrial function can take weeks to recover postcardioversion, accounting in part for the delayed embolic risk. TEE is particularly effective at detecting atrial thrombi and shows that slow velocities in the atrium and appendage are an important risk factor for embolism and clot. All are associated with the finding of spontaneous echo contrast and atrial stunning postcardioversion. The ultimate role of TEE in management is not yet fully defined. The insights these and other studies provide to our understanding of atrial physiology and the appropriate management of atrial fibrillation are reviewed.