In this work, the content of matrix metalloproteinase-9 (MMP-9) in the blood serum was studied as an independent predictor of recurrence of atrial fibrillation after catheter radiofrequency ablation (CRA). The results of analyzes of patients with long-persistent form of atrial fibrillation (LPAF) lasting more than one year and resistant to drug therapy are analyzed. All patients before the procedure of catheter radiofrequency ablation measured the concentration of MMP-9 and evaluated its association with the recurrence of arrhythmias at the end of the postoperative period. For this, enzyme-linked dual enzyme immunoassay was used. 35 patients with LPAF were examined. The follow-up period was 16.2 + 5.7 months, in 12 (34.3%) patients there was a relapse of the arrhythmia after the ablation procedure. The basic content of MMP-9 was higher in patients with relapsed arrhythmia (261.3 + 35.3 and 202.46 + 27.6 ng/ml, respectively, P <0.05). Multivariate analysis showed that parameters such as MMP-9 content, a history of atrial fibrillation and a diameter of the left atrium were independent predictors of arrhythmia recurrence. Thus, MMP-9 is an independent predictor of arrhythmia recurrence after performing the procedure of catheter radiofrequency ablation in patients with atrial fibrillation.