Radiofrequency catheter ablation or modification of the atrio-ventricular junction is an effective therapy of drug refractory supraventricular tachyarrhythmias (ST). Higher endothelin (ET) levels were observed during nonsustained STs. We aimed to examine the effect of sustained STs and the applied rate-control therapy on plasma ET levels. Twenty-two patients (12 men; mean age, 64.4 +/- 13.2 years; ejection fraction, 41.8 +/- 11.2%; New York Heart Association (NYHA) class I: 3 cases, NYHA II: 11 cases, and NYHA III: 8 cases) suffering of atrial fibrillation (n = 11), atrial flutter (n = 7), atrial paroxysmal tachycardia (n = 3), or sinus tachycardia (n = 1) were studied, having coronary artery disease (n = 8), dilative cardiomyopathy (n = 5), or no underlying diseases (n = 9). All groups went under catheter ablation (same protocol, duration: 35 +/- 10.3 mins; rate before ablation, 100-170/min in every case; after ablation, 70-80/min in Groups I and II and 70-90/min in Group III). A pacemaker (PM) was implanted 2 months before ablation in Group I (n = 9) and during ablation in Group II (n = 7). No PM was implanted in Group III (n = 6). A control group (n = 13; 7 men; mean age, 66.15 +/- 6.7 years) with sinus rhythm got a PM without ST and ablation. Blood samples were collected from the cubital vein immediately before (control), and 5 mins and 24 hrs after ablation. Plasma ET-1 and big ET-1 levels were measured after immunoprecipitation with Western blot analysis. There were no differences between plasma ET-1 levels in the ST groups and the control group (Groups I, II, and III vs. control group: 0.66 +/- 0.04 fmol/ml, 0.93 +/- 0.12 fmol/ml, and 0.68 +/- 0.05 fmol/ml vs. 0.50 +/- 0.05 fmol/ml, respectively; P < 0.05). Comparing the control, 5-min, and 24-hr samples, ET-1 levels decreased significantly after supraventricular tachycardia ablation in Groups I and III (control vs. Group I, 5 mins and 24 hrs: 0.66 +/- 0.04 fmol/ml vs. 0.50 +/- 0.04 fmol/ml and 0.29 +/- 0.05 fmol/ml; control vs. Group III, 24 hrs: 0.68 +/- 0.05 vs. 0.34 +/- 0.05 fmol/ml; P < 0.05). No plasma big ET-1 changes were measured in any of the groups. The rapid decrease of ET levels after catheter ablation suggests that a high ventricular rate can be a trigger of ET production. PM implantation procedure seems to interfere with the ET decrease in ST patients.