We aimed to characterize changes in interventricular septum (IVS) motion and any relationship between them and the pulmonary-to-systemic flow ratio (Qp/Qs) in adult patients with atrial septal defect (ASD). Patients and controls were studied using colour tissue Doppler imaging (TDI). The septum length (SL) and distance from the colour change point (CCP) on the IVS to the aortic valve (the CCP distance) were measured on parasternal long axis views. Values normalized for body surface area, and the CCP distance to SL ratio, were calculated. Qp/Qs values were correlated with CCP distance, normalized CCP distance and CCP distance:SL ratio. Statistically significant differences in CCP distance, normalized CCP distance and CCP distance:SL ratio were found between the two groups. In the ASD group, there was no correlation between Qp/Qs and the echocardiographic measurements. The point between the motions in two different directions from the IVS shifted toward the apex in ASD patients compared with controls, and may be a mechanism involved in paradoxical septal motion.