Most patients with atrial fibrillation (AF) can be treated slowly with high doses of reassurance and education. There is, however, a small group of higher-risk patients who have both AF and heart failure that require prompt aggressive action.The CASTLE HTx trial, presented at the European Society of Cardiology congress, studied catheter ablation of AF vs medical therapy in these sick patients with advanced heart failure. The results were stunningly positive for ablation.CASTLE HTx is single-center trial done at a major referral center for heart transplantation in Bad Oeynhausen, Germany. The investigators screened just over 900 patients who were referred for assessment of eligibility for heart transplant or left ventricular assist device (LVAD) who also had symptomatic AF. About 20% (n = 194) of these patients were randomly assigned to either primary AF ablation or continued medical therapy.The average age of these mostly male patients was 62 and 65 years, in the ablation vs medical therapy groups, respectively. The average left ventricular ejection fraction was 25% in the medical therapy group and 29% in the ablation arm. One third had New York Heart Association (NYHA) functional Class II heart failure while two thirds had Class III-IV heart failure. Baseline medical therapy was excellent in both groups.The primary endpoint was a composite of death from any cause, implantation of an LVAD, or urgent heart transplantation.Two experienced electrophysiologists performed the ablation procedures, 68% of which were pulmonary vein isolation (PVI) alone.