Objective: To assess emergency department (ED) utilization and physician preparedness for infants with single ventricle (SV) physiology between stage 1 and stage 2 surgical palliation. Study design: Records of infants with SV physiology discharged after stage I palliation between July 2006 and June 2009 were retrospectively reviewed. Next, a cross-sectional survey of registered ED physicians in Michigan was performed. Results: Thirty-three of 42 patients (79%) required 65 ED visits, most commonly presenting with respiratory distress (35%). Six patients died in the ED; 35 other visits resulted in hospital admission, 4 requiring urgent surgery or catheterization. Median initial hospital stay in those with ED visits was significantly longer (21 days; IQR, 17-45 days) than those without (12 days; IQR, 5.5-24 days) (P =.032). Three hundred seventy-six of 915 surveyed ED physicians responded. Most (72%) were unsure of the acceptable range of arterial oxygen saturation for these infants, and 58% felt "uncomfortable" or "worried" about their treatment. Despite these concerns, 59% deemed education in SV physiology as low priority. Conclusions: Between stages I and II, infants with SV physiology utilized the ED frequently, often with high disease acuity. Most ED physicians surveyed appeared underprepared for these infants. These findings underscore the need for educational efforts aimed at increasing ED preparedness.