Background Mortality rate for heart transplantation for patients with hypoplastic left heart syndrome (HLHS) has improved, but there is a considerable wait until a suitable donor is available. Thus it is important to examine the duration of survival and risk factors for early death in patients with HLHS who did not undergo surgical intervention. Methods and Results Twenty-six consecutive patients were studied retrospectively. Duration of survival and the 14 following variables were investigated: date of birth, body weight at birth, cardiothoracic ratio, ascending aorta diameter, interatrial communication size, coarctation of the aorta, tricuspid regurgitation, anatomic subtype (patency) of mitral and aortic valve, arterial blood gas findings (pH, PaO₂ , SaO₂ , PaCO₂ , base excess), and ST depression in the electrocardiogram. Twenty patients survived <60 days (group A) and 6 patients survived beyond 60 days (group B). The duration of survival (mean [SD]) was 60 (151) days overall (1 patient is currently alive at 783 days). The long-term survivors (beyond 60 days) increased significantly after 1991 (P < .05). Coarctation of the aorta was a significant risk of early death (<60 days) (P < .05). Interatrial communication size was significantly smaller in group B than in group A (P < .05). The mean pH and base excess were significantly lower in group A than in group B. The other 9 variables showed no significant difference between the 2 groups. Conclusions There was a significant correlation of long-term survival with stabilized ductal blood flow without coarctation of the aorta, adequate restriction of interatrial communication without severe hypoxemia, and no metabolic acidosis. (Am Heart J 1999;137:535-42.)