Objective To evaluate the feasibility and effect of transthoracic echocardiography(TTE)on guiding the occlusion of the soft-rim atrial septal defect(ASD).Methods Sixty two patients with the soft-rim ASD were enrolled.The size of ASD was measured and rim of ASD was observed by TTE on various views by using color Doppler system with tissue harmonic function before occlusion,and filmy rim of ASD with flapping which could not sustain occluder was eliminated.The size of occluder was selected by integratively judging the size of ASD and"sustainable diameter of ASD"The waist size of occluder was measured after releasing occluder and compared with the longest diameter of ASD and"sustainable diameter of ASD"measured by TTE.Results The longest diameter of ASD measured by TTE before occlusion was 11-35 mm[average(21.6±5.2)mm],the "sustainable diameter of ASD"was 15-37 mm[average(25.6±5.(J)mm],the size of selected occluder was 18-44mm[average(30.7±5.5)mini and the waist size of released occluder was 13-35 mm[average(24.2±5.6)mm].Fine correlation was existed between the longest diameter of ASD measured by TTE and the waist size of released occluder(r=0.86,P＜0.000I).Morever,improved correlation was found between the"sustainable diameter of ASD"measured by TTE and the waist size of released occluder(r=0.89,P＜0.0001).Occluder was firmly fixed without falling in all patients.Conclusions TTE with tissue harmonic function can be used to measure the size of soft-rim ASD and the"sustainable diameter of ASD".It is a feasible,and effective method on guiding occlusion of soft-rim ASD.