Background: Atrioventricular septal defect(AVSD) and double outlet right ventricle(DORV) with normally related great arteries and normal ventricular sizes are associated with a good long-term prognosis after biventricular(BV) repair. The outcome of cases with a borderline small left ventricle(bLV) is unclear. The purpose of the study was to retrospectively determine echocardiographic predictors of successful BV repair in fetuses with AVSD or DORV with a bLV.Methods and Results: From 1991 to 2004, 24 fetuses with AVSD plus bLV and 24 with DORV plus bLV were identified. Fetal echocardiographic parameters comparing BV repair versus single ventricle(SV)palliation were obtained, including the presence or absence of an apex-forming bLV was recorded. A bLV was defined as a right ventricular/left ventricular end-diastolic dimension ratio between 2 and 4 SDs for gestational age. The overall survival from fetal diagnosis was 21%(5/24) for AVSD/bLV and 13%(3/24) for DORV/bLV. Of 11 liveborns with AVSD/bLV and 8 liveborns with DORV/bLV, 6 underwent BV repair(5 survivors), 7 SV palliation(3 survivors), and 1 cardiac transplant. Five infants receiving compassionate care only were excluded from the analysis. Parameters such as ratio of valve annuli, ventricular end-diastolic dimensions, degree of valve regurgitation, and the presence of endocardial fibroelastosis were not too predictive of outcome. The presence of an apex-forming bLV was the only predictor of BV repair(6/6 BV repair vs 2/8 SV palliation, P< .05). Conclusions: Prenatally diagnosed AVSD or DORV with bLV has a very poor prognosis. An apex-forming bLV predicts successful BV repair and is an important prognostic indicator. Background: Atrioventricular septal defect (AVSD) and double outlet right ventricle (DORV) with normally related great arteries and normal ventricular sizes are associated with a good long-term prognosis after biventricular (BV) repair. The outcome of cases with a borderline small left The purpose of the study was to retrospectively determine echocardiographic predictors of successful BV repair in fetuses with AVSD or DORV with a bLV. Methods and Results: From 1991 to 2004, 24 fetuses with AVSD plus bLV and 24 with The presence of absence of an apex-forming bLV was recorded. A bLV was defined as a right ventricular / left ventricular end-diastolic The overall survival from fetal diagnosis was 21% (5/24) for AVSD / bLV and 13% (3/24) for DORV / bLV. Of 11 liveborns with AVSD / bLV and 8 liveborns with DORV / bLV, 6 underwent BV repair (5 survivors), 7 SV palliation (3 survivors), and 1 cardiac transplant. Five infants receiving compassionate care were were excluded from the analysis. Parameters such as ratio of The presence of an apex-forming bLV was the only predictor of BV repair (6/6 BV repair vs 2 / 8 SV palliation, P <.05). Conclusions: Prenatally diagnosed AVSD or DORV with bLV has a very poor prognosis. An apex-forming bLV predicts successful BV repair and is an important prognostic indicator.