Objective To evaluate the application value of 70kV combine iterative reconstruction technique in pediatric cardiac CT compared with 80kV.Methods 73 patients with clinical diagnosis of congenital heart diseaseswere randomly divided into two groups,underwent cardiac CT with 80kV(groupA)and 70kV(groupB),respectively.Both groups were examined by perspective ECG-gated Multidetector-row CT(MDCT),automatic tube current modulation(CARE Dose 4D),and the raw data were underwent SAFIRE(grade 3)iterative reconstruction.CT attenuation value and image noise were measured at muscle of back,the root of ascending aorta,main pulmonary artery,the lumen of left and right ventricular,and fat of chest wall.And CNR was calculated.The image quality was scaled by 5 points(in great arteries and ventricles),or by 3 points(in coronary arteries),it was evaluatedby 2 radiologists back to back.Record CTDIvol,DLPand calculate and compare the effective doses(ED)between 2 groups.Results There were statistically significant differences in CT attenuation value of the great vessels and heart chambers,and image noise between the two groups(P < 0.05).CT attenuation value and image noise of group B were increased about 25-32%compared with group A,but CNR showed no difference between the two groups.(P > 0.05).The image qualities of both groups could meet the need of diagnosis.There were no difference in image quality scale points between the two groups.(P > 0.05)The great vessels(k=0.823),heart chambers(k=0.795),the initial and proximal segments of coronary arteries(k=0.750).CTDIvol(t=8.967,P<0.05),DLP(t=8.773,P<0.05)and ED(t=10.053,P<0.05)of group B were lower than group A by 44%.Conclusion 70kV combine iterative reconstruction technique in pediatric cardiac CT showed significantly decreased radiation dose while the image quality remained reliable for congenital heart disease.