If a patient will enter the laboratory in SVT or if SVT will be induced by initial catheter placement, the "onset of SVT time" is designated "0 min." Additionally, the investigators will compare the antegrade effective refractory period of the accessory pathway (antegrade APERP), ventricular effective refractory period (VERP), atrial effective refractory period (AERP), AH interval, and cycle length of circus movement tachycardia (CMT-CL).