This study evaluates the stress ECG test as a non-invasive method of risk stratification in patients with WPW syndrome. For the non-invasive part a stress electrocardiogram on a treadmill is used. The invasive comparison is made with an electrophysiological study (EPS) in the catheterization laboratory. Nowadays the gold standard for measuring the antegrade effective refractory period of the accessory pathway is the invasive EPS.