Some. The Watchman has nothing to do with AF or with its modification, control, or its prevention. It's just a plug. A mesh inserted into the left atrial appendage to block off that shallow 'cave' or grotto. This is where the highest risk of stroke from AF lies, about 90% of all strokes related to AF happen in the LAA. The Watchman, if properly installed, and if it seals off with endothelial growth, will not allow blood to enter it. No blood, no clot.