The Glenn procedure is an open-heart surgery that reroutes blood flow in babies born with only one working pumping chamber instead of the usual two. Surgeons disconnect the large vein carrying blood back from the head and upper body and attach it directly to the artery leading to the lungs, allowing that blood to pick up oxygen without the heart having to pump it there. It is typically performed around 4 to 6 months of age and serves as the second stage in a three-surgery plan to rebuild circulation in children with single-ventricle heart defects.
How Blood Flow Changes After Surgery
In a normal heart, the right ventricle pumps oxygen-poor blood to the lungs, and the left ventricle pumps oxygen-rich blood to the body. Children born with a single functional ventricle lack that two-pump system, so the one working chamber has to do double duty. That puts enormous strain on the heart and mixes oxygen-rich and oxygen-poor blood together, leaving the child with lower oxygen levels than normal.
The Glenn procedure reduces that workload. By connecting the superior vena cava (the vein draining the upper body) directly to the pulmonary artery (the vessel leading to the lungs), blood from the head, arms, and upper torso flows passively into the lungs using only the force of gravity and the body’s own venous pressure. The heart no longer has to pump that portion of blood to the lungs, which means the single ventricle can focus more of its energy on sending oxygenated blood out to the body. After the surgery, a child’s oxygen saturation typically sits around 75% to 85%, which is lower than a healthy child’s level but a meaningful improvement over the pre-surgical baseline.
Which Heart Defects Require It
The Glenn is not used for one specific diagnosis. It applies to a range of congenital heart defects that all share the same core problem: only one ventricle is large or strong enough to pump effectively. The most common of these is hypoplastic left heart syndrome, where the left side of the heart is severely underdeveloped. Other conditions include tricuspid atresia (a missing or malformed valve between the right chambers), double inlet ventricle (where both upper chambers feed into a single lower chamber), pulmonary atresia with an intact wall between the ventricles, unbalanced atrioventricular canal defects, and certain forms of transposition of the great arteries.
What ties these conditions together is that a two-ventricle repair is not possible. The surgical team instead commits to a staged approach that gradually separates the oxygen-poor and oxygen-rich blood streams using passive flow rather than a second pumping chamber.
Where It Fits in the Three-Stage Plan
The Glenn is the middle step in a sequence of three surgeries developed to rebuild circulation for single-ventricle patients.
- Stage 1: Norwood procedure. Performed in the first days or weeks of life, this surgery creates a pathway for the single ventricle to pump blood to the body and places a temporary shunt to keep some blood flowing to the lungs.
- Stage 2: Glenn procedure. Done around 4 to 6 months of age, this removes the temporary shunt and connects the upper-body veins directly to the lungs. This is sometimes called a “bidirectional Glenn shunt” or a “hemi-Fontan,” depending on the surgical technique used.
- Stage 3: Fontan procedure. Usually performed between ages 2 and 4, this final surgery redirects the remaining blood (from the lower body) to the lungs as well, completing the separation of oxygen-poor and oxygen-rich blood.
Each stage is timed to match the child’s growth and the natural changes in lung resistance that happen in the first years of life. The Glenn cannot be done before about 2 months of age because pressure in the lungs is still too high for blood to flow passively into them. Data from a national pediatric cardiology registry shows the lowest surgical risk when the Glenn is performed between 3 and 6 months after the Norwood. Babies who had the procedure before 4 months of age had higher mortality, often because of coexisting medical issues, while those who waited past about 5 months also faced increased risk.
What the Hospital Stay Looks Like
After the Glenn, children typically spend about three days in the intensive care unit. This is followed by several more days in a regular hospital room before discharge. Compared to the Norwood (stage 1), the Glenn recovery is generally shorter and less complicated. The child will have a chest incision from the open-heart approach, and the medical team monitors heart function, oxygen levels, and fluid balance closely during those first days.
Because blood now flows to the lungs passively rather than being pumped, any buildup of fluid around the lungs can interfere with that flow. Drainage tubes are placed during surgery to manage this risk, and they are removed once output drops to safe levels. Some children also experience temporary swelling in the face or upper body as circulation adjusts to the new plumbing.
Life Between the Glenn and the Fontan
After the Glenn, only the upper body’s blood flows directly to the lungs. Blood returning from the legs and abdomen still mixes with oxygenated blood in the single ventricle, which is why oxygen saturations remain in the 75% to 85% range. Your child may still have a noticeable bluish tint to the lips or fingernails. This is expected and does not mean the surgery failed.
The period between the Glenn and the Fontan (typically 1.5 to 3 years) is often described by parents as the most stable stretch of their child’s early life. The heart’s workload has been significantly reduced, and many children gain weight, hit developmental milestones, and become noticeably more active during this window. Regular cardiology visits and imaging are part of this period, as the surgical team tracks heart function and lung artery growth to determine readiness for the final Fontan stage.
Long-Term Outlook
Short-term survival after the Glenn is high at experienced pediatric heart centers, and most children go on to complete the full three-stage sequence with the Fontan. The long-term picture depends heavily on the underlying heart anatomy. A study tracking patients over four decades found that 40-year overall survival after a Glenn (in those who did not go on to a Fontan) was about 40%. Patients whose single ventricle had a left-sided structure fared significantly better, with 40-year survival reaching 73%, compared to roughly 23% at 30 years for those with a right-sided ventricle doing the pumping.
These numbers reflect patients who stayed at the Glenn stage rather than completing the full surgical pathway, so they represent a specific subset. For children who complete all three stages, the trajectory can look quite different. Still, single-ventricle heart disease is a lifelong condition. Even after all surgeries are complete, these children need ongoing cardiology care throughout their lives. Heart rhythm problems, exercise limitations, and gradual changes in heart or liver function are all possibilities that the care team monitors over time.
The Glenn procedure does not create a normal heart. What it does is take a heart that is dangerously overworked and give it a more sustainable way to circulate blood, buying time and stability for the child to grow toward the next surgical stage.