BACKGROUND: Trans-catheter closure of atrial septal defects (ASD) with the Amplatzer Septal Occluder (ASO) device is safe and effective, but concern over erosions has increased. Devices are placed in growing children but septal growth after ASOs is ill-defined. Understanding the device relationship to cardiac structures as a child grows may help us understand erosions. OBJECTIVE: To define (1) how preprocedural septal measurements change after ASO and (2) the effect of somatic growth on these dimensions. METHODS: Data were collected retrospectively. Echocardiograms were reviewed and rims measured prior to ASO, immediately after ASO, and at follow-up. Demographic, procedural and device data were collected. RESULTS: Thirty-three patients were enrolled; mean age 5.2 +/- 3.2 years with 4.0 +/- 2.2 years follow-up. All septal measurements decreased after ASO. Thirty-one of 33 devices (94%) contacted the aortic root after ASO; all remained in contact at follow-up with only the IVC rim growing significantly over time. Change in BSA predicted an asymmetric septal growth with increases in superior (P = 0.01) and IVC (P = 0.005) rims and no increase in aortic or AVV rims. No episodes of erosion occurred. CONCLUSIONS: ASDs in young children are not central in the septum, but proximate to the aorta. After ASO, the device remains in close proximity to the aorta. With somatic growth, the septum grows asymmetrically, and device position relative to the aorta is constant. Our study was not powered to detect rare serious adverse events such as erosion, but aortic rims were consistently zero and yet no events occurred. (c) 2015 Wiley Periodicals, Inc.