Background In China,transthoracic echocardiography(TTE)is popularly used for pre-intervention examination for atrial septal defect(ASD)and for guiding ASD closure.However,the ability to determine ASD size and the safety and efficacy of TTE for guiding ASD closure still has not been widely accepted This study aimed to evaluate the efficacy and safety of TTE used before,during and after transcatheter ASD closure with Amplatzer septal occluders(ASO).Methods Sixty-eight subjects(15 men and 53 women;mean age(33.7±17.3)years)were enrolled.TTE was used to measure the diameters and guide transcatheter closure of ASD.The ASD was examined by long-axis view,basal short-axis view,apical four-chamber view and the subcostal view to observe position.diameter and reIation with neighbouring structures.The largest diameter was selected as the reference diameter.Patients were divided into 3 groups according to the ASD reference diameter:22 subjects with ASD diameter 4-14 mm(group A):21 subjects with ASD diameter 15-20 mm(group B);and 25 subjects with ASD diameter 21-33 mm(group C).Results ASD was occluded successfully in groups A and B.In group C.occlusion failed in 2 cases;1 case remained with a 3-mm residual shunt sustained untiI 6-month follow-up.However,at 6-month follow-up,no case of thromboembolism,ASO dislocation or death occurred in the three groups.The diameter of ASD measured bv TTE could accurately predict the ASO size that could successfully occlude the ASD.especially in patients with ASD＜20 mm.The ASD diameter measured by TTE correlated well with ASO size(r=0.925,P＜0.001:r=0.976,P＜0.001;r=0.929,P＜0.001 respectively).Conclusions ASD diameter measured by TTE can accurately estimate the size of the ASO needed for successful closure of ASD.The larger the ASD,the much larger the ASo needed.TTE is a satisfactory guiding imaging tool for ASD closure.