Sixty nine cases of paroxysmal supraventricular tachycardia (PSVT) were submitted to electrophysiological studies. The prevalent data in different types of PSVT are as follows: 49% are atrioventricular reentry tachycardia (AV-RT), 14.5% atrioventricular nodal reentry tachycardia (AVN-RT), 28% AV + AVN-RT, and 8.5% of other types. Altogether 77% in this group have atrioventricular accessory bypass, in which about half of them are concealed ones. Electrocardiographic characteristics during tachycardia give hints to diagnosis: (1) AV-RT has the fastest heart rate, with 62% greater than 200 beats/min, and 82% greater than 188 beats/min; (2) retrograde P waves can be detected in 64% cases of AV bypass; (3) 50% of AV-RT show bundle branch block pattern QRS. Since accessory pathways are the majority in our country, the importance of treatment is stressed.