### Learning objectives Ventricular pre-excitation is an electrocardiographic finding characterised by a delta wave and short PR interval. It is estimated that 1 in 1000 people will exhibit this pattern on the ECG; however, the true prevalence is likely under-represented because at least half of known patients with pre-excitation do not develop symptoms.1 This ECG pattern indicates the presence of an accessory atrioventricular pathway (AP), an alternate electrical connection between atria and ventricles bypassing the normal His-Purkinje system. APs can conduct in antegrade direction, retrograde direction or both. Approximately 60%–75% of these pathways are considered ‘manifest’, meaning they are capable of antegrade conduction, and can inscribe the classic pre-excitation pattern on the ECG, and the rest are ‘concealed’, meaning they are only capable of retrograde conduction, cannot produce pre-excitation, but can still participate in atrioventricular (AV) re-entry tachycardias. The ini