e know that the risk of stroke is increased in patients with trial fibrillation (AF), presumably because stagnant blood ow within the left atrium leads to thrombus formation. mportantly, 90% of thrombi, when seen by echocardiograhy in patients with nonrheumatic AF, are located in the eft atrial appendage (LAA) (1,2). Standard treatment of atients with AF is anticoagulation with warfarin. If war...