During the index procedure of catheter ablation (CA) for atrial fibrillation (AF), it is important to assess whether other atrial or ventricular tachyarrhythmias are coexisted. Their symptoms were often attributed to residual tachycardias after successful elimination of AF by CA and these tachycardias are also known as one of non-pulmonary vein foci initiated AF. This study examined the coexistence of other sustained tachyarrhythmias of the patients who underwent radiofrequency (RF) CA for AF. Methods & Results: 457 consecutive patients (373 males, aged 53.3짹11.5 years) who underwent RFCA for AF were investigated. Atrial and ventricular programmed stimulation (PS) with or without isoproterenol infusion were performed and spontaneously developed tachycardias were analyzed. There were 17 (3.7%) patients diagnosed to have other arrhythmias; 6 atrioventricular nodal reentrant tachycardias (AVNRTs) which all were the slow–fast type and three patients were revealed during PS, one before PS, and another 2 months later after PS. 5 atrioventricular reentrant tachycardias (AVRTs), utilized left posteroseptal (n=4) and parahisian bypass tract (n=1). 4 atrial tachycardias (ATs) originated from crista terminalis (n=3) and the ostium of coronary sinus (CS, n=1). Sustained ventricular tachycardias (VTs) in 2, one from apical posterolateral wall of LV in normal heart and one from anterolateral wall in underlying myocardial infarction (MI). Most of tachycardias were not clinically documented. None had structural heart diseases, except one patient with VT in MI. Two patients had the triple tachycardias, AVNRT, AVRT, and AF. The other had AF, AT, and idiopathic VT. All associated tachycardias were successfully eliminated by RFCA. Conclusions: 3.7% patients with AF had coexisting sustained tachycardias in whom RFCA was performed. Identification of these tachycardias by programmed stimulation before RFCA for AF should be done for increasing the efficacy of the first ablation session and for making the patients symptom free from all the arrhythmias