@#Objective    To investigate the prognosis and risk factors of mild to moderate or moderate atrioventricular valve regurgitation (AVVR) after Fontan operation. Methods    A total of 34 patients with mild to moderate or moderate AVVR who accepted Fontan operation and atrioventricular valve (AVV) repair between 2004 and 2018 in our center were selected as an AVV repair group. The patients in the same period were matched as a control group by the ratio of 1 : 1-2. Finally 99 patients were included into this study, including 64 males and 35 females, with an average age of 63.4±36.3 months and weight of 17.3±6.7 kg. Grades of AVVR decreased more than 1 was defined as significant improvement. Endpoints of the study were death, Fontan takedown, AVV replacement. Risk factors including Fontan procedures, AVV repair procedures, cardiac anatomy were analyzed. Results    Patients were followed up for 1.5 (0.3-4.0) years. Overall mortality was 15.2%. Most (82.4%) of AVV repair group accepted single AVV repair procedure while partial annuloplasty was the most common (52.9%). With the extension of follow-up, the degree of AVVR in the whole group showed a gradually increasing trend (r=0.352, P=0.000). Mild to moderate AVVR improved spontaneously after Fontan operation, while moderate AVVR did not. AVV repair could improve the degree of AVVR after moderate regurgitation, without increasing the surgical mortality, and regurgitation significantly decreased in 8.8% patients. AVV repair was not effective for mild to moderate AVVR and would increase surgical mortality. Conclusion    AVV function shows a gradual downward trend after Fontan operation. AVV repair is effective for moderate AVVR, does not increase mortality, but the degree of improvement is limited. AVV repair is not effective for mild to moderate AVVR and increases surgical mortality.