Sykehuset Telemark performs every year approximately 800 Holter ECG examinations. Approximately 200 of these are on the indications tachycardia, and in about 170 patients the examination does not discover any tachycardia Patients who were examined in the period from August 1. 2004 to November 1. 2005 with a negative Holter are mailed a letter with information of the min invasive electrophysiological examination, and an offer of volunteer participation. Patients given their informed consent are then according to waiting list called for the mini-invasive EP-study.