Objective:To study the alteration and clinical significance of plasma endothelin-1(ET-1) after transcatheter closure of atrial septal defect(ASD). Methods:Radioimmumoassay was used to measure plasma concentration of ET-1 in 40 ASD patients before,30 minutes after and three days after transcatheter closure of ASD. Results:The plasma level of ET-1 in ASD patients was remarkably higher than that of the control,no matter the ASD patients’ pulmonary arterial pressure was increased or not. In ASD patients,the plasma concentration of ET-1 correlated with the pulmonary arterial pressure,pulmonary to systemic flow ratio(Qp/Qs) and the size of ASD(r = 0.868, r = 0.746 and r = 0.670,respectively(P < 0.01). The plasma level of ET-1 in ASD patients after ASD closure decreased significantly compared with the level before ASD closure. And the plasma concentration of ET-1 in ASD patients three days after ASD closure was lower than that at 30 minutes after ASD closure. Conclusion:The endothelium function in patients with ASD can be improved after transcatheter closure of ASD. The plasma level of ET-1 may be used as a marker for evaluating the effect of transcatheter closure of ASD.