Transcatheter occlusion of ostium secundum atrial septal defects (ASD) with the buttoned device has been shown to be feasible, effective, and safe. The final decision to implant the device is largely based on the balloon sizing of the ASD during cardiac catheterization. Only subjective criteria of ASD size and the septal rims on echocardiography have been used before catheterization, balloon sizing, and transcatheter occlusion. The purpose of this study was to determine whether objective echo criteria could be developed to predict successful occlusion of the ASD. During a 46-month period ending August 1992, 29 children with secundum ASD were evaluated for transcatheter occlusion. The device was successfully implanted in 15 (group A); in the remaining 14 children, this procedure could not be performed (group B). Preocclusion echos were analyzed by independent investigators who had no knowledge of outcome of the procedure. Echo parameters studied included size of ASD, length of atrial septum (LAS), and size of the superior and inferior rims in precordial and subcostal views and maximum jet width by color flow mapping. From these measurements several ratios were derived, and the data were compared. A smaller (p < 0.05) ASD was present in the group of patients with successful implantation of the device; LAS was similar (p > 0.1) in both groups. A lower (p < 0.05) ratio of ASD to LAS and a higher (p < 0.05) ratio of the superior and inferior septal rims to ASD were associated with the group of patients with successful implantation of the device.(ABSTRACT TRUNCATED AT 250 WORDS)