['The aim of this study is to evaluate the mid-term clinical and functional outcomes of maze surgery in symptomatic refractory lone atrial fibrillation (AF) patients.', 'Between March 2008 and January 2013, 39 highly symptomatic patients [mean age 51 ± 10 (mean ± standard deviation); 95% CI, European Heart Rhythm Association class III-IV] underwent maze surgery for lone AF. Biatrial ablations were performed with bipolar radiofrequency and cryoenergy, according to a maze III lesion set (modified by omitting the intercaval line in 5 of 39 patients). Mean ejection fraction was 51 ± 9% (range 17-60), <45% in 10 patients (26%). Seventeen of 39 patients (44%) had persistent, 22 of 39 patients (56%) long-standing persistent AF, and 35 of 39 patients (90%) had previous transvenous ablations (median = 2; range 0-8). No patient had concomitant structural heart disease.', 'A minimally invasive approach was adopted in 22 patients (56%). Major complications were 1 mediastinitis, 1 re-exploration for bleeding and 2 pacemaker (5%) implantation. At a mean follow-up of 29.4 ± 14.2 months, freedom from arrhythmias was 92 and 93% at 24 and 36 months, respectively. Freedom without antiarrhythmic drugs was 75 and 85% at 24 and 36 months, respectively. Ejection fraction normalized in all cases, from 51.3 ± 9% to 61.1 ± 3% (P < 0.001) overall, and from 37.0 ± 10% to 60.3 ± 3% (P < 0.001) when ≤ 45% preoperatively. AF-related symptoms score decreased to class I in 36 patients (93%). No early or late stroke occurred.'] Does maze surgery normalize left ventricular function in patients with persistent lone atrial fibrillation?