In infants with aortic arch hypoplasia and small left-sided cardiac structures, successful biventricular repair is dependent on the adequacy of the left-sided structures. Defining accurate thresholds of echocardiographic indices predictive of successful biventricular repair is paramount to achieving optimal outcomes. We sought to identify pre-operative echocardiographic indices of left heart size that predict intervention-free survival in infants with small left heart structures undergoing primary aortic arch repair to establish biventricular circulation (BVC). Infants ≤2 months undergoing aortic arch repair from 1999 to 2010 with aortic and/or mitral valve hypoplasia, (Z-score ≤−2) were included. Pre-operative and follow-up echocardiograms were reviewed. Primary outcome was successful biventricular circulation (BVC), defined as freedom from death, transplant, or single ventricular conversion at 1 year. Need for catheter based or surgical re-intervention (RI), valve annular growth, and significant late aortic or mitral valve obstruction were additional outcomes. Fifty one of 73 subjects (79%) had successful BVC and were free of RI at 1 year. Seven subjects failed BVC; four of those died. The overall 1 year survival for the cohort was 95%. Fifteen subjects underwent a RI but maintained BVC. In univariate analysis, larger transverse aorta (p = 0.006) and aortic valve (p = 0.02) predicted successful BVC without RI. In CART analysis, the combination of mitral valve (MV) to tricuspid valve (TV) ratio ≤0.66 with an aortic valve (AV) annulus Z-score ≤−3 had the greatest power to predict BVC failure (sensitivity 71%, specificity 94%). In those with successful BVC, the combination of both AV and MV Z-score ≤−2.5 increased the odds of RI (OR 3.8; CI 1.3–11.4). Follow-up of non-RI subjects revealed improvement in AV and MV Z-score (median AV annulus changed over time from −2.34 to 0.04 (p < 0.001) and MV changed from −2.88 to −1.41 (p < 0.001), but residual mitral valve stenosis and aortic arch obstruction were present in one-third of subjects. In this cohort of infants requiring initial aortic arch repair with concomitant small left heart structures, successful BVC can be predicted from combined echocardiographic indices. In this complex population, 1 year survival is high, but the need for RI and the presence of residual lesions are common.