AbstractPercutaneous transvenous closure of atrial septal defects (ASDs) has become feasible in recent years, as later‐generation devices have largely overcome initial difficulties in device deployment and complication rates. The Amplatzer septal occluder (ASO) is one such device that we have used extensively and is, in our opinion, the most versatile and practical to use. It is capable of closing defects up to 40 mm in diameter via a relatively low‐profile delivery sheath. More importantly, the ASO may be easily withdrawn into the sheath after deployment but prior to release, which is essential in safely closing difficult defects where successful positioning on the initial deployment is not guaranteed. In this article based on our experience, review of the literature, and communications with other operators, we describe the various problems encountered in closing atrial septal defects and make suggestions as to the best way of overcoming these difficulties. Cathet Cardiovasc Intervent 2002;57:508–524. © 2002 Wiley‐Liss, Inc.