Transcatheter closure of secundum atrial septal defect (ASD) < 21 mm in diameter with adequate septal margins, assessed by transthoracic echocardiography (TTE) was attempted using Sideris buttoned device under fluoroscopic and TTE guidance in 27 patients (age range 5-35 years). The stretched diameter of ASD estimated by balloon sizing at cardiac catheterization was, on an average, 3 mm larger than assessed on TTE. A 25 to 50 mm second-generation Sideris device could be successfully implanted in 24 patients, with disappearance of left-to-right shunt, assessed by colour flow mapping on TTE in 17 patients. Residual shunt of 0.12-0.54 L/min/m2 was seen on day one in 7 patients which increased on follow-up in 3 patients over a period of 12 months. The maximum shunt in one patient was 1.1 L/min/m2. On follow-up (14.5 +/- 3.8 months), the device was in a stable position in all patients evaluated by fluoroscopy and TTE, and intracardiac ultrasound study in two patients. The procedure was unsuccessful in 3 patients, due to unbuttoning of the device in one and recurrent slippage of the device through the ASD in two patients. Mitral regurgitation was detected in 5 patients on follow-up (mild in 4 and moderate in 1). There was no mortality and none of the patients required any surgical intervention. It is concluded that transcatheter closure of some selected cases of secundum ASD can be safely and effectively done using Sideris buttoned device through a small sheath; however, a centering device is likely to close larger defects with less interference with mitral valve function.