Normally, the electrical signals which coordinate heartbeat travel through the atria (the top two chambers of the heart) to the ventricles (the bottom two chambers). These signals travel through the atrioventricular (AV) node, which is the electrical pathway connecting the two portions.

In people with Wolff-Parkinson-White syndrome, there is an extra (accessory) atrioventricular conduction pathway. This extra pathway bypasses the normal conduction delay of the AV node, and it may cause a form of "supraventricular tachycardia."

This is a rapid heart rate initiated above the ventricles. The type of supraventricular tachycardia experienced by people with Wolff-Parkinson-White syndrome is called "re-entry." The extra-electrical pathway in Wolff-Parkinson-White can often be located precisely.

Wolff-Parkinson-White occurs in approximately 4 out of 100,000 people, and is one of the most common causes of fast heart rate disorders (tachyarrhymthmias) in infants and children.

The frequency of the episodes of rapid heart rate varies from person to person. Patients with Wolff-Parkinson-White may have isolated episodes of rapid heart rate, frequent episodes (occurring once or twice a week), or they may never have symptoms. In the latter case, the condition is often discovered accidentally when a physician is reviewing an ECG requested for some other purpose.