Abstract: AIM: To investigate the effectiveness and safety of transthoracic closure of atrial septal defects (ASD) in the treatment of ASD. METHODS: A new kind of occluder device and its delivery system were designed. The occluder device was delivered by an outer sheath, an inner sheath and a delivery rod through the fourth intercostal space and right atrial wall to occlude the ASD. A total of 386 patients (mean age 11.8 years, range: 1-79 years) were treated using this transthoracic procedure, and clinical data were analyzed. RESULTS: Mean stretched diameter of ASD was 20.4 (range: 4-38 mm). Occluder devices were successfully implanted in 382 patients, and 22 patients received two devices because of multiple fenestrations in the atrial septum. The entire procedure time varied from 35 to 62 (44±7.4)min and the intracardiac maneuver time varied from 9 to 17 (12±1.9)min. Transthoracic echocardiography showed that the success rate of total occlusion was 98.9% 24 h after implantation. Device embolization during implantation occurred in one case. The device was retrieved and the ASD was closed surgically. Cerebral bleeding occurred at night in one successfully occluded ASD case and the patient was effectively treated neurosurgically. CONCLUSION: Transthoracic closure of ASD is effective and safe with surgical ease in the treatment of the majority of ASD patients.