Abstract: Objective: To evaluate the value of the real-time three-dimensional echocardiograph(RT-3DE) in the diagnosis of atrial septal defect(ASD) and guidance of transcatheter closure.Methods: Twenty-one patients with ASD were diagnosed by two-dimensional ultrasound and RT-3DE,the defect panorama was showed by three-dimensional imaging,the area of which was measured.The whole process of operation were guided by RT-3DE and fluoroscopy,and the blockage effects were evaluated after operation.The correlation between the maximum diameter of waist occluder and defect area measured by RT-3DE were studied.Results: All operations were successfully completed.Transthoracic RT-3DE could clearly display the shape,size,position of ASD and occluder releasing process.The differences of the ASD areas between RT-3DE measuring and maximum diameter of the waist minus 2 mm calculating were not statistically significant(P > 0.05).This differences between RT-3DE and X-ray in identifying the position and status of sheath,and occluder releasing were not statistically significant(P > 0.05).Conclusions: The method of transthoracic RT-3DE in guiding the closure of ASD is feasible,which can avoid the radiation of X-ray and has application value.