. Among its many consequences, the one that carries the greatest burden with regard to morbidity is embolic stroke. The rate of ischemic stroke among patients with nonvalvular AF averages 5% per year, a fivefold increase compared with that of people without AF 2 . The risk of stroke increases with age. The annual risk of stroke attributed to AF is 1.5% in subjects aged 50 to 59 years and 23% in those aged 80 to 89 years. Importantly, the left atrial appendage (LAA) is the primary site of thrombus formation as a precursor to embolic stroke in nonvalvular AF patients 1 . In these patients, anticoagulation with warfarin has become standard medical therapy, reducing the risk of stroke by ~60%. Nonetheless, the long-term use of warfarin carries several drawbacks and complications, including non-tolerance, non-adherence, interactions with food and other medications, a very narrow therapeutic range, and an increased risk of bleeding 3 . In addition, oral anticoagulation is contraindicated in up to 40% of patients with AF who are at risk for stroke. Accordingly, several surgical and percutaneous techniques have been explored to occlude the LAA for stroke prevention. As an alternative to surgical closure, percutaneous transcatheter LAA closure (LAAC) represents a novel approach to prevent strokes in highrisk patients with nonvalvular AF and contraindications to long-term oral anticoagulant therapy. In selected patients, dedicated LAAC devices such as Watchman (Atritech Inc, Plymouth, Minn) and the Amplatzer cardiac plug (ACP; AGA Medical Corp., Minneapolis, MN, USA) have shown encouraging initial results. For instance, The Watchman Left Atrial Appendage System for Embolic Protection in Patients With AF (PROTECT AF) trial — the only randomized study to address this issue — has shown the therapeutic noninferiority of LAAC when used as an alternative to longterm warfarin in preventing stroke (with less intracranial hemorrhages) in patients with a CHADS 2 score ≥1 4 . The events in the Watchman group occurred early and were related to the procedure, predominantly pericardial effusion and procedural stroke related to air embolism. Besides the aforementioned clinical criteria for percutaneous LAAC and the assessment of stroke risk by CHADS 2 and the CHA 2 DS 2 -VASc scores, anatomical characteristics of the LAA should be taken into account when selecting candidates for this procedure. The left atrial appendage is a long, tubular and hooked structure which has a narrow junction with the venous component of the atrium. In adults, the mean volume of the LAA is approximately 5.2 ml, with orifice diameters ranging from 5 to 40 mm. There is considerable inter-individual variability in the size and shape of the LAA. Functions of the LAA include modulation of sympathetic and parasympathetic tone, decompression of the left atrium in the setting of elevated atrial pressure and volume overload, production of natriuretic peptides (atrial natriuretic peptide, brain natriuretic peptide) and contribution to the diastolic filling of the left ventricle 5