Endothelin-1 (ET-1) is a potent endogenous arrhythmogenic substance. The aim of our study was to investigate the changes of serum ET-1 and big-endothelin levels in patients suffering from spontaneous, incessant ventricular tachyarrhythmias. The 11 consecutive patients' (mean age, 59 +/- 11 years) underlying diseases were ischemic heart disease, valvular heart disease, dilated cardiomyopathy, primary electrical disease, and arrhythmogenic right ventricular dysplasia in five cases, three cases, one case, one case, and one case, respectively. The mean ejection fraction was 39 +/- 14%, New York Heart Association functional status was I, II, and III in two cases, four cases, and five cases, respectively. Ventricular tachycardias (VT) were detected in five patients, ventricular fibrillation (VF) in three patients, and VT + VF in three patients. VTs terminated spontaneously in two cases. Six patients required multiple external cardioversion/defibrillation shocks, while implantable cardioverter defibrillators terminated all sustained arrhythmias successfully in four cases. Blood samples were collected during arrhythmias and 24 hours (control) following the last VT/VF episode. Serum ET-1 and big-endothelin levels were measured with western blot analysis after immunoprecipitation. Serum ET-1 and big-endothelin levels were significantly higher during the last VT/VF compared with the control period (ET-1, 65.8 +/- 26.8 fmol/mL versus 53.9 +/- 22.3 fmol/mL, P < 0.05; big-endothelin, 115.2 +/- 39.3 fmol/mL versus 89.2 +/- 25.1 fmol/mL, P < 0.05). There was a negative correlation between the age and big-endothelin level measured at both times (during VT/VF, r = 0.94, P < 0.05; control, r = 0.91, P < 0.05). In conclusion, serum big-endothelin and ET-1 levels were significantly higher during incessant VT/VF, which can be a cause of multiple arrhythmia recurrence.