The authors report two cases of secondary displacement of an Amplatz occluder of isolated ostium secundum atrial septal defects. The displacement was observed at 1 month and the prosthesis removed at 3 months. To the best of the authors' knowledge, these are the first two reported cases of secondary displacement of this type of device. The main risk factor in the two cases was the absence of a subaortic septal remnant observed at surgical removal. This anatomical characteristic can be identified by transoesophageal echocardiography, but was poorly assessed by transthoracic echocardiography. Three-dimensional transoesophageal echocardiography should improve selection of atrial septal defects suitable for percutaneous treatment by better identification of their form and anatomical characteristics.