vena cava is ligated from the heart and connected to the pulmonary circulation. at this time, the blalock-taussig or sano shunt is taken down. the lungs are no longer exposed to systemic arterial pressures, but much lower venous pressures. although venous blood from the upper half of the body is no longer mixing with oxygenated blood in the right ventricle, there is still venous mixing from the lower half of the body, leading to some degree of oxygen desaturation. fontan procedure the final procedure, the fontan procedure, completes the repair of the hypoplastic left heart. although there are several variations, the functional effect is to redirect venous blood from the lower body (through the inferior vena cava) away from the right atrium to the pulmonary artery. this should eliminate any mixing of oxygenated and deoxygenated blood in the right ventricle. the right ventricle performs the traditional job of the left, supplying the body with oxygenated blood, while the passive systemic venous pressure performs the traditional job of the right, passing deoxygenated blood to the lungs. fetal surgery interventions performed during fetal development are under investigation. in fetuses with hypoplastic left ventricles and an intact interatrial septum, percutaneous atrial septostomy has been attempted. prognosis 95% of untreated infants with hlhs die in the first weeks of life. early survival has improved since the introduction of the norwood procedure. since there are no long-term studies of hlhs adults, statistics are usually derived from post-fontan patients; it is estimated that 70% of hlhs patients may reach adulthood. prognosis is dependent upon the health of the child, as there is an increased demand on respiratory and heart rate in infants during common childhood illnesses. this fragile population has little cardiac reserve to accommodate these demands and provide hemodynamic stability during illnesses. children with hlhs and other comparable single-ventricle conditions, as a group, have poorer neurodevelopmental outcomes than their healthy peers. deficits in language, executive functioning, and higher rates of anxiety and depression disorders have been demonstrated. some of these outcomes may be a consequence of genetic factors associated with hlhs, and others may be modifiable through changes to procedures and to the healthcare environment. there is an emerging clinical consensus around the importance of continuous neurodevelopmental surveillance from the earliest years into adulthood. additionally, a recent meta-analysis comparing twenty-two studies showed that 64.7% of the studies reported delayed motor development in children with single ventricle physiologies, such as hypoplastic left heart syndrome. as is true for patients with other types of heart defects involving malformed valves, hlhs patients run a high risk of endocarditis, and must be monitored by a cardiologist for the rest of their lives to check on their heart function. heart transplantation may be indicated, typically after fontan completion. one multi-center study (of patients undergoing the fontan from 1993 to 2001) reported a 76% 1-year survival rate in patients who survived to transplant. future of stem cell therapies a systematic review found 23 articles, published since 2010, as well as nine relevant clinical trials related to congenital heart disease and recent advances in stem cell therapies. pre-clinical research has focused on several types of stem cells including: mesenchymal stem cells (mscs), autologous umbilical cord blood cells, c-kit+ cardiac stem cells, and neonatal thymus mesenchymal stem cells. these cell types have shown the ability to differentiate into cardiac tissue making them ideal for cardiac regenerative therapy. the first use of autologous umbilical cord blood cells was done at the mayo clinic in 2015 and was found to increase right ventricular function in the patient after their procedure. the first use of cardiac progenitor cells occurred in the transcoronary infusion of cardiac progenitor cells in patients with single-ventricle physiology (ticap) trail of 2011. ongoing trials there are several ongoing studies testing the feasibility and efficacy of stem cell therapies for single ventricle diseases such as hlhs. these trials focus on what are the most effective stem cells, what is the best timing in the 3-stage repair, and what is the optimal delivery method. phase iib trial testing the efficacy of intramyocardial injections umbilical cord blood cells during stage ii (glenn) repair. phase i trial testing the efficacy of autologous cord blood cell infusion during stage 1 (norwood) repair within two-to-three days of birth. the elpis trial is a phase i/iib open pilot testing the efficacy and safety of intramyocardial donor human mesenchymal stem cell injections in patients during stage 2 (glenn) and stage 3 (fontan) repairs. phase i trial testing the efficacy of umbilical cord blood intramyocardial injections during stage 2 (glenn) repair. the perseus study is a phase ii trial testing the efficacy of intracoronary infusions of cardiac progenitor cells and evaluating function 3-months post-treatment. apollon study is a phase iii clinical trial testing the efficacy and safety of intracoronary injections of autologous cardiac stem cells during stage 2 (glenn) or stage 3 (fontan) repair. child study is a phase i clinical trial testing the feasibility and safety of intramyocardial injections of c-kit+ cells during stage 2 (glenn) repair. it is important to keep in mind that patients with hlhs are at increased risk of developing heart failure as adults. it remains unknown if these potential therapies would reduce the future risk of heart failure in these patients.