Radiofrequency catheter ablation was performed in 21 patients who had congenital heart diseases associated with accessory pathway (AP)-mediated tachycardia (14 patients), with atrioventricular (AV) nodal reentrant tachycardia (4 patients), with intraatrial reentrant tachycardia (1 patient), with coexistent AP mediated tachycardia and AV nodal reentrant tachycardia (1 patient) and with coexistent AV nodal reentrant tachycardia and atrial tachycardia (1 patient). Congenital heart diseases diagnosed were seven with Ebstein's anomaly and six with septal defect; the others included patent ductus arteriosus, supravalvular aortic stenosis and left superior vena cava-coronary sinus fistula. Incidence of multiple APs (26.7 vs. 7.7%, P = 0.027), antidromic tachycardia (20.0 vs. 2.9%, P = 0.011), tachyarrhythmia-related syncope (26.7 vs. 7.2%, P = 0.022) and cardiac arrest (13.3 vs. 0%, P = 0.001) was higher in patients with AP and congenital heart diseases. Longer procedure (3.9 +/- 0.7 vs. 2.4 +/- 1.3 h for AP, P = 0.001; 3.0 +/- 0.7 vs. 2.5 +/- 0.8 h for AV nodal reentrant tachycardia, P = 0.001), and radiation exposure times (102 +/- 27 vs. 35 +/- 23 min for AP, P = 0.001; 62 +/- 23 vs. 20 +/- 11 min for AV nodal reentrant tachycardia, P = 0.001) were necessary to achieve a high success rate (95%) in patients with congenital heart disease.