BACKGROUND: The prognosis for hypoplastic left heart syndrome (HLHS) has greatly improved over the past years, but there is still a significant risk of interstage mortality. Tricuspid valve regurgitation (TR) is known to be a risk factor for interstage mortality. We hypothesized that a modified Blalock-Taussig (BT) shunt with a smaller diameter would lead to a reduction in ventricular volume loading with a consequent reduction in TR. METHODS: A retrospective review of all patients with HLHS who had a Norwood procedure in our institution between 2006 and 2011 was performed. Patient demographic, echocardiographic, cardiac magnetic resonance imaging, and operative data were reviewed. The impact of BT shunt diameter on severity of TR at the time of bidirectional cavopulmonary connection (BCPC) was analyzed. RESULTS: Sixty-four neonates with HLHS underwent a Norwood procedure with a BT shunt. Thirty-two had a 3.5-mm BT shunt (3.5-mm group), and 32 had a 3.0-mm BT shunt (3.0-mm group). Survival to BCPC was 53 of 64 patients (83%) overall, with 25 of 32 patients (78%) in the 3.5-mm group and 28 of 32 (88%) in the 3.0-mm group (p = 0.51). The prevalence of significant TR (moderate or higher) before BCPC was 9 of 25 patients (36%) in the 3.5-mm group and 2 of 28 patients (7%) in the 3.0-mm group (odds ratio = 7.3; 95% confidence interval: 1.4-38; p = 0.018). Tricuspid valve repair was performed in 4 of 25 patients (16%) in the 3.5-mm group and 2 of 28 patients (7%) in the 3.0-mm group (p = 0.21). CONCLUSIONS: A smaller-diameter BT shunt reduces the prevalence of significant TR at the time of BCPC. Further investigation and long-term follow-up are required to determine potential complications of this surgical strategy.