Catheter closure of secundum atrial septal defect (ASD) using the Amplatzer septal occluder (ASO) is a potential alternative for open surgical repair. However, the large profile of the device obtained immediately after closure continues to raise some concerns regarding its long-term safety. To evaluate the changes in the profile of the device after being deployed, transesophageal echocardiography was performed in 70 patients (17 men and 53 women) who underwent catheter closure of ASDs immediately after and at 6-month follow-up. The median age at closure was 16 years (range 1.9 to 75) and the median size of the ASD as assessed by transesophageal echocardiography was 14 mm (range 3 to 25). The thickness (profile) of the device was assessed in the 4-chamber, short- and long-axis views of the interatrial septum, and measured at its middle and at the junction of the waist with the disc at its 2 ends. Seventy-three devices were deployed in the 70 patients. The median size of the device was 19 mm (range 8 to 34). Complete closure was achieved in 81.4% and 91.4% immediately after and at 6-months follow-up, respectively. The thickness of the device at its middle decreased from 12.2 +/- 4.3, 12.2 +/- 3.7, and 12.5 +/- 4.3 mm in the 4-chamber, short- and long-axis views to 6.5 +/- 2.0, 6.3 +/- 1.9, and 6.5 +/- 2.2 mm, respectively. The thickness of the device at its superior, inferior, anterior, and posterior edges also decreased by 41.8% +/- 14.0% to 43.7% +/- 9.8%. The changes in the thickness were related to device size. Larger devices were thicker after being deployed. We conclude that the thickness of the ASO decreases by 42% to 48% within 6 months after deployment, resulting in a lower profile.