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Objective Assessment of right ventricular function in patients with atrial septal defect (ASD) is difficult. The Doppler myocardial performance index (MPI) may provide a method of assessing function in these patients. The purposes of this study were to evaluate the right ventricular function and its changes in patients with ASD after transcatheter closure of ASD. Methods MPI, defined as the sum of isovolumic relaxation time and isovolumic contraction time derived by ejection time, was measured from tricuspid inflow and right ventricular outflow; Doppler velocity profiles recorded during routine echocardiography. Twenty nine patients ( 13 men, 16 women;mean age 25.28 ± 12.69, range 6 to 57 years) were diagnosed to secundum ASD [the stretched diameters of ASD were from 9 To 36 (24.91 ±7.98) mm], and had a successfully placed Amplatzer septal occluder (ASO) (the sizes of ASO were from 11 to 40 mm ); there were 81 sex-matched, age-matched healthy people (control group 41men, 40 women; mean age 29.02 ± 14.22, range 4 to 45 years).MPI was measured again on 3 days and 1 month after closure of ASD. Change in the study group was assessed and compared to the control subjects with structurally normal hearts. A complete 2- dimensional and Doppler echocardiographic examination was performed in all study groups. Results 1) The isovolumic relaxation and isovolumic contraction times [respectively(77.59 ± 14.39)ms vs (60.93 ± 12.94)ms, P＜0.0001; (28.28 ± 10.88)ms vs (23.64 ± 9.01)ms, P=0.027] were prolonged, and ejection time [(260.65 ± 21.86 )ms vs (271.85 ± 21.92)ms, P=0.033] was shortened in patients with ASD compared with that in control subjects, resulting in a marked increase in the MPI(0.40 ± 0.07 vs 0.31 ± 0.05, P＜0.0001) from normal values; 2) by Pearson's correlations, the MPI had no correlation with heart rate and blood pressure in control subjects and patients with ASD, but it correlated positively with age in patients with ASD; 3) by Pearson's correlations, the MPI correlated positively with the diameter of ASD and pulmonary artery pressure; 4) after transcatheter closure of ASD, the MPI decreased markedly. Conclusions 1) MPI is a conceptually new, simple, and reproducible Doppler index in patients with ASD; 2) MPI is free from the effect of age, heart rate and blood pressure; (3) MPI appears to be relatively dependent on changes in the diameter of ASD and pulmonary artery pressure; 4) the right ventricular function was improved after transcatheter closure of ASD.