Background A significant shortening of the corrected QT interval (QTc) in addition to parasympathetic denervation after cardioneuroablation (CNA) was recently demonstrated in patients with vagally mediated bradyarrhythmias and normal QTc range. This study assessed the effects of CNA on ventricular repolarization and heart rate by using QTc measurements in 2 patients with long QT syndrome (LQTS). Methods The case series included 2 consecutive patients with significant sinus bradycardia and refractory paroxysmal atrial fibrillation (AF). All atrial ganglionated plexus (GP) sites in addition to pulmonary vein isolation were successively targeted by using electrogram-guided strategy. QTc was calculated on 12-lead ECG before the procedure (time point 1), at post-ablation 24 h (time point 2), and at the last follow-up visit (time point 3), respectively. Results In the first case, QTc (Bazett) shortened from 612 to 551 msec between time points 1 and 2 and was 419 msec in time point 3. Similarly, QTc (Bazett) shortened from 480 to 401 msec between time points 1 and 3 in the second case. In both cases, minimum and mean heart rates were significantly increased after ablation. The parameters of which are used to estimate both sympathetic and parasympathetic changes in heart rate variability were significantly decreased after ablation. There were no arrhythmia-related symptoms during follow-up. Conclusions The present case series reports a new ablation strategy systematically targeting autonomic GPs in LQTS patients. CNA shortens QTc (through sympathetic modulation) and increases heart rate. Although promising, these preliminary results need to be confirmed in the larger prospective study.