The mRNA expression levels of MMP-9, Bcl-2, and Bax in the muscle cells of the right atrium from each group were detected to find that mRNA levels of MMP-9 and Bax in patients with AF were extremely higher than those of patients with sinus rhythm, and mRNA levels of TIMP-1 and Bcl-2 were steeply lower than those of patients with sinus rhythm (P < 0.05). This evidence concerns the gene MMP9 and atrial fibrillation.