The analysis and the characterization of atrial fibrillation (AF) requires, in a previous key step, the extraction of the atrial activity (AA) free from 12-lead electrocardiogram (ECG). This contribution proposes a novel non-invasive approach for the AA estimation in AF episodes. The method is based on blind source extraction (BSE) using high order statistics (HOS). The validity and performance of this algorithm are confirmed by extensive computer simulations and experiments on realworld data. In contrast to blind source separation (BSS) methods, BSE only extract one desired signal, and it is easy for the machine to judge whether the extracted signal is AA source by calculating its spectrum concentration, while it is hard for the machine using BSS method to judge which one of the separated twelve signals is AA source. Therefore, the proposed method is expected to have great potential in clinical monitoring. electrocardiogram (ECG), atrial fibrillation, blind source separation (BSS), blind source extraction (BSE)