Left atrial "onion-ring" thrombosis during atrial fibrillation ablation.

![Figure][1] [![Graphic][3] ][3] We report the case of a huge left atrial (LA) thrombus formation during LA ablation. A single transseptal puncture was used as usual. The first St. Jude SL0 sheath was positioned in the LA and flushed and perfused with saline solution. The second SL0