Radiofrequency (RF) catheter ablation of the atrioventricular node (AVN) and implantation of a ventricular pacemaker can improve cardiac performance in patients with congestive heart failure (CHF) and uncontrolled atrial fibrillation (AF). Alternatively, RF catheter modification of the AVN has been proposed to slow ventricular response during AF without requirement for permanent pacing. Among 44 consecutive patients (mean age 69.7 +/- 10.2 years) with drug resistant chronic AF, 22 (group I) had AVN ablation with permanent ventricular pacemaker implantation, while 22 patients had attempted AVN modification. Complete AV block was obtained in all group I patients while only seven (32%) AVN modification patients (group II) had permanent slowing of ventricular rate. Among patients in group I, mean left ventricular ejection fraction (EF) increased from 32.2% +/- 8.8% before ablation to 41.9% +/- 14.6% 4-weeks postablation (P < 0.01); exercise tolerance time (ETT) increased from 2.9 +/- 2.2 minutes to 4.5 +/- 2.9 minutes (P < 0.01); and quality-of-life score decreased from 66.1 +/- 22.6 to 36.9 +/- 17.1 (P < 0.01). By comparison, there was only a small increase in ETT in the seven successful group II patients (2.4 +/- 1.8 minutes to 3.0 +/- 1.9 minutes; P < 0.05) and there was no significant change in EF or quality-of-life. While AVN ablation can occasionally have transient adverse effects, it is more effective than AVN modification for improving cardiac performance in selected patients with CHF and AF.