BACKGROUND/OBJECTIVE:Secondary subaortic stenosis (SSS) can occur after surgery for various congenital heart defects with or without initial left ventricular outflow tract obstruction (LVOTO). The objective of this study was to highlight the anatomical lesions and surgical procedures associated with the development of SSS after surgery on defects without initial LVOTO. METHODS:A retrospective study of 4710 patients was performed (1984-2005). The criterion for inclusion was a fixed subaortic obstruction requiring surgery, after an open- or closed-heart operation. The criterion for exclusion was an LVOTO at the time of the first operation. RESULTS:Twenty-eight patients were studied. The mean age at initial surgery was 32 months (4 days-47 years; median: 2 months). SSS occurred after three main types of surgery: repair of coarctation of the aorta, repair of AVSD and LV-aorta rerouting for double outlet right ventricle or transposition of great arteries. The mean delay of occurrence was 4.4 years (2 months-19 years). Frequently associated initial anatomical conditions were coarctation of the aorta (40%), lesions of the mitral valve (32%), bicuspid aortic valve (21%) and left superior vena cava (LSVC) (14%). Preoperative anatomical lesions of the LVOT were present in 93% of the cases. After the initial operation, only one patient had a mean echo-Doppler pressure gradient across the LVOT>20 mmHg. SSS was most frequently a subaortic membrane (n=23). The mean pressure gradient across SSS at the time of reoperation was 47+/-29 mmHg. Five patients developed a second SSS after 7.4 years (mean). One patient developed a third SSS. No patient died. When compared with patients without SSS, significant risk factors for SSS were low age at surgery (32 vs 74.9 months, p<10(-4)), pre-existing coarctation of the aorta (40 vs 10%, p<10(-4)), bicuspid aortic valve (21 vs 6%, p=0.002) and LSVC (14 vs 4%, p=0.02). CONCLUSIONS:SSS development is multifactorial, depending on initial anatomical lesions and initial surgery. Low age at initial surgery, coarctation of the aorta, bicuspid aortic valve and LSVC significantly increase the risk of SSS. These elements warrant long-term follow-up for early detection of SSS.