Transcatheter closure of secundum atrial septal defect(ASD) with a "buttoned" double-disk device is feasible, effective and safe method as an alternative to surgical closure. Stretched diameter of ASD, determined by balloon sizing is generally used as a guide to prediction of success or selection of device size used for transcatheter closure of ASD. To test whether other non-invasive assessment of ASD size can provide an alternative method for a stretched diameter, we studied the relationship between various measures of ASD in 22 adult patients with ASD. Although transthoracic echocardiographic horizontal or vertical diameter of ASD, the maximal diameter of ASD measured at operation and pulmonary-to systemic flow ratio(Qp : Qs), the stretched diameter had no significant correlation with other measurements. It is conclused that other assessments of ASD size can not be used as adjuncts in the estimation of the stretched ASD diameter, which in turn can be used for prediction of success or selection of device size for occlusion of the ASD.