Sudden cardiac death may be the first event in the history of Wolff-Parkinson White syndrome: this is a very rare event although as ablation of the accessory pathway avoids this risk a potentially malignant form of the disease needs to be detected. Electrophysiological studies are the most reliable method. These may be performed by a trans-oesophageal or endocavity approach from the age of six to seven years onwards. Whilst it is rare to detect a potentially malignant form the results of these studies more often enable the person to play sports or continue their job without offering radio-frequency ablation. The former however is indicated when tachycardia is induced in children over 12 years old and in adults.