A 56-year-old male with no previous significant medical history initially presented to his general practitioner for a routine health check prior to starting a new occupation. An electrocardiogram (ECG) was taken that was found to be unusual and, hence, a referral to cardiology outpatients was made. Initial recommendation was made for ablation therapy based on the finding of Wolff-Parkinson-White (WPW) syndrome. After a successful procedure, the patient developed significant palpitations with haemodynamic compromise that required emergency direct current (DC) cardioversion. Subsequent re-investigation found a previously unmasked uncommon form of accessory tachyarrhythmia. This case report highlights the finding of Mahaim pathway in a patient initially treated for WPW syndrome.