The outlook for patients with hypoplastic left heart syndrome has dramatically improved over the past two decades. Universally fatal only 25 years ago, since that time outcomes for staged palliation have shown consistent improvement. Recent reports show that eight to nine patients from every ten can now leave the hospital after the Norwood procedure.1 Attrition following the Norwood procedure, nonetheless, remains significant, with from five to fifteen percent of patients dying between the first and second stages of the Norwood sequence.1–4 Only three-quarters of the patients undergoing surgery for hypoplastic left heart syndrome survive after five years, even at the centres reporting the best outcomes for the Norwood procedure.1,5 In addition to the deaths, some patients are unable to progress through the three stages of reconstruction, and may require cardiac transplantation, or have no options for further therapy. There are many causes for these mortalities and morbidities following the Norwood procedure, including elevated pulmonary vascular resistance, cardiac arrhythmias, coronary arterial insufficiency, right ventricular failure, right ventricular volume overload due to shunt-dependent physiology, and tricuspid valvar regurgitation. Many of these factors are interrelated, and may form feedback loops, which serve to propagate their adverse effects on patients with hypoplastic left heart syndrome.