Ablation of accessory pathways (AP) is one of the most often performed procedures in pediatric electrophysiology. In pediatric patients these procedures are mostly performed in anaesthesia or sedation. In some of these patients who are referred for electrophysiologic (EP) study, we could observe disappearance of the preexcitation, i.e. antegrade conduction of an AP during introduction of sedation. As a suppression of AP conduction capacities has been reported as negative side effect of propofol and other anaesthetics, the aim of this study was to evaluate risk factors for drug-induced suppression of AP conduction properties. Consecutive, pediatric patients with Wolff–Parkinson–White (WPW) pattern referred for EP study in the period of 2016–2017 were reviewed in retrospect. Patients with complex congenital heart disease were excluded. An entire chart review including ECG, bicycle stress testing, and periprocedural data was performed. In 4 of 37 patients included into the study, loss of preexcitation could be observed during sedation. Data analysis showed weaker conduction capacities of the AP as a risk factor (p = 0.009). Interestingly, absolute (p = 0.11) or adjusted to body weight (p = 0.92) drug doses were not a relevant risk factor. Patients with WPW and weaker conduction capacities of the AP, as implied by an early disappearance of preexcitation during exercise stress testing, seem to be more prone to drug-induced suppression of an AP.