This research is going to recruit 200 consecutive patients with a history of atrial fibrillation for 180-360 days who intend to undergo catheter ablation. The day before catheter ablation, serum FGF-23 level will be detected. Echocardiogram and left atrial CT scan will also be performed on the day before catheter ablation. All patients will be routinely follow up in the outpatient department by cardiologists every month for 1 year. If patients complain about palpitations, fatigue, or other symptoms related to arrhythmia, Holter monitoring will be performed. Patients will also be advised to see their doctor anytime they have these symptoms and to undergo a 12-lead ECG examination or 24-hour Holter monitoring. In asymptomatic patients, 24-hour Holter monitoring or 7-day cardiac event recording will be performed every three months after the procedure. The endpoint for follow-up is the recurrence of atrial fibrillation, which is considered to be any episode of AF/AFL/AT after a blank period of 3 months after the procedure of catheter ablation. Those who develop recurrence of AF during follow up will be assigned to recurrence group, and those who do not develop recurrence of AF during follow up will be assigned to non-recurrence group. Comparison of the serum FGF-23 level between the two groups will be carried out in order to investigate the relationship between serum FGF-23 level and the recurrence of AF.