Background: Age and sex are known to influence the mechanisms of PSVT but large scale data regarding this subject is limited. Also, data regarding the mechanisms of PSVT in the Korean population is limited as well. In this study, we sought to investigate the differing mechanisms of PSVT according to age and sex in 3176 Korean patients. Methods: Database of 3176 patients diagnosed with PSVT and referred for electrophysiologic study from 1986 to 2004 was analyzed. The mechanisms of PSVT was classified as atrioventricular reentrant tachycardia(AVRT) due to WPW syndrome(WPW), AVRT due to concealed bypass tract(CBT), atrioventricular nodal reentrant tachycardia(AVNRT), atrial tachycardia(AT), or sinoatrial reentrant tachycardia. Patients with atrial flutter or atrial fibrillation were excluded. Results: The average age was 40.7짹16.0(1-90) with 53.3% of the patients being males. The average age of females was signficantly higher than that of males.(43.0짹16.1 vs 38.6짹15.6, p < 0.001) Over all, the dominant mechanism of tachycardia was AVRT at 62.6%(WPW: 31.1%, CBT: 31.5%) compared to AVNRT at 34.1% and AT at 3.1%. This was mainly due to the predominance of AVRT(74.2%) in males. The mechanisms of PSVT differed according to gender with 63.2%(1257/1988) of AVRT patients being males where as 64.6%(700/1084) of the AVNRT patients were females. The distribution of PSVT mechanisms differed according to gender. In males the proportion of AVNRT:CBT:WPW was 22.7%:36.1%:38.1% whereas in females the proportion was 47.2%:26.3%:23.0%. Age had a significant influence upon the mechanism of PSVT in both sexes with increasing proportion of AVNRT with age and decreasing proportion of AVRT with age. AVRT was the dominant mechanism of PSVT in all age groups in males where as AVNRT became the dominant mechanism of PSVT for females over 50 years of age. Conclusions: The mechanism of PSVT differs significantly according to age and gender. This may be due to increased degeneration of accessory pathway with age and difference in the conduction properties of the accessory pathway according to gender. In Koreans, the overall dominant mechanism of PSVT was AVRT mainly due to its predominance in males.