PURPOSE: We accidentally found out the decrease of color M-mode propagation velocity of LV inflow(Vp) in several Atrial septal defect(ASD) infants. The aim of this study was to identify it in more number of patients, and to find out the relationship of it to clinical characteristics and other cardiac function study results. METHODS: The present study was conducted on 16 isolated secundum ASD infants with defect diameter greater than 3 mm(L group), 10 infants with a defect diameter less than 3 mm(S group) and 11 infants with no structural abnormal findings(N group), among infants who visited the Pediatric Department of Soonchunhyang University Hospital and underwent a echocardiographic examination from April 2001 through June 2003. The systolic function tests via parasternal long axis, and other diastolic function tests were done at the same time. RESULTS: The mean ages of these three groups(L group, S group and N group) were 0.35+/-0.34 years, 0.22+/-0.22 years and 0.45+/-0.27 years, respectively. The Vp values were 48.42+/-10.84 cm/sec, 65.26+/-16.25 cm/sec, 65.28+/-13.36 cm/sec in groups, and significant difference between L group and other 2 groups(P=0.001). The only affecting variable to Vp values is defect area. There was significant causal relationship between them(P= 0.000). CONCLUSION: We identified the decrease of Vp in ASD infants, and it was linearly related to defect area size. It may be result of early diastolic ventricular interdependence in ASD.