An atrioventricular septal defect (AVSD) is a heart defect present at birth where holes exist between the chambers of the heart and the valves that control blood flow between those chambers don’t form correctly. It’s sometimes called an AV canal defect. The result is that oxygen-rich blood mixes with oxygen-poor blood and too much blood gets pumped to the lungs, forcing the heart to work harder than it should.
How a Normal Heart Compares to One With AVSD
A healthy heart has four separate chambers: two upper chambers (atria) and two lower chambers (ventricles). Walls called septa divide the left and right sides, keeping oxygen-rich blood separate from oxygen-poor blood. Two one-way valves sit between the upper and lower chambers, the mitral valve on the left and the tricuspid valve on the right, opening and closing with each heartbeat to keep blood flowing in the right direction.
In AVSD, the walls between the chambers fail to fully develop during pregnancy, leaving holes where the upper and lower walls would normally meet in the center of the heart. The valves can also be malformed or fused into a single shared valve. Because pressure is higher on the left side of the heart, blood gets pushed through these holes from left to right, flooding the lungs with excess blood flow. Over time this extra workload can damage the blood vessels in the lungs and strain the heart muscle.
Complete vs. Partial AVSD
AVSD exists on a spectrum, and the type determines how severely blood flow is disrupted.
Complete AVSD is the most serious form. There is a large hole in the center of the heart that allows blood to flow freely between all four chambers. Instead of two separate valves, there is one common valve that bridges both sides of the heart. This valve often has leaflets (flaps) that don’t close tightly, so blood leaks backward with each heartbeat. Babies with complete AVSD typically develop symptoms early in life because the abnormal blood flow is significant from the start.
Partial AVSD involves some but not all of the defects seen in the complete form. Usually there is a hole in just the wall between the upper chambers, near the center of the heart. Two separate valves are present, but one of them, typically the mitral valve on the left side, doesn’t close completely. This allows blood to leak backward from the lower left chamber into the upper left chamber. Symptoms tend to be milder and may not appear until later in childhood or even adulthood.
An intermediate or transitional form falls between the two. It features two separate valve openings but has holes in both the upper and lower chamber walls.
Connection to Down Syndrome
AVSD is strongly associated with Down syndrome (trisomy 21). Among babies with Down syndrome who have a congenital heart defect, AVSD is the most common type, accounting for roughly 44% of cases. Not all babies with AVSD have Down syndrome, but the overlap is significant enough that genetic testing is a routine part of the diagnostic workup.
Signs in Infants
The symptoms depend on whether the defect is complete or partial. Babies with complete AVSD often show signs within the first weeks to months of life as the lungs become overwhelmed with excess blood flow. Common signs include rapid or labored breathing, poor feeding, sweating during feedings, and failure to gain weight at a normal pace. The skin may look pale or bluish, especially around the lips and fingertips. A heart murmur is usually detectable with a stethoscope.
Partial AVSD can go undetected longer because the blood flow abnormality is less severe. Some children grow normally for years before the extra strain on the heart begins to cause noticeable fatigue or breathing difficulty.
How AVSD Is Diagnosed
The primary tool is an echocardiogram, an ultrasound of the heart. It can reveal the hallmark signs of AVSD: a common valve where two separate valves should be, holes in the chamber walls, and a disrupted appearance at the center (crux) of the heart where the walls and valves normally come together. Color Doppler ultrasound adds another layer by showing the direction and speed of blood flow, making it possible to see blood leaking backward through a faulty valve or streaming through a hole between chambers.
AVSD can sometimes be detected before birth during a routine prenatal ultrasound, though complete AVSD is easier to spot prenatally than the partial form. After birth, if a murmur or symptoms raise suspicion, a postnatal echocardiogram confirms the diagnosis and helps classify the type.
Surgical Repair
AVSD does not resolve on its own. Surgery is the definitive treatment for both complete and partial forms, and timing matters.
For complete AVSD, most centers perform elective repair between 3 and 6 months of age. Operating in this window avoids two risks: permanent damage to the blood vessels in the lungs from prolonged overcirculation, and the higher surgical risk seen in very young infants under 3 months. The goal of surgery is to close the holes with one or two patches and separate the single common valve into two functioning valves.
Two main techniques are used. The modified single-patch approach closes the defect with one piece of material, while the two-patch technique uses separate patches for the upper and lower holes. A meta-analysis of 724 patients found that the single-patch method required about 23 to 29 fewer minutes on the heart-lung bypass machine, but long-term outcomes, including reoperation rates, mortality, and hospital stay, were comparable between the two approaches.
Partial AVSD repair can sometimes be scheduled later, depending on how much the valve is leaking and how well the child is growing. The surgery still involves closing the hole and repairing the malformed valve.
Recovery and Long-Term Outlook
After surgery, most children recover in the intensive care unit for several days before moving to a regular hospital room. The total hospital stay varies but typically spans one to two weeks for uncomplicated cases.
Long-term survival after repair has improved considerably with modern surgical techniques, but the repaired heart does require lifelong monitoring. The most common reason for a second surgery is a leaky left-sided valve, which accounts for 4 to 15% of reoperations. For patients who leave the operating room with a well-functioning valve, freedom from reoperation at five years is around 96%. When significant valve leakage remains after the initial repair, that number drops to about 75% at five years.
Many children who undergo successful repair go on to live active, full lives. Regular cardiology follow-up is important because valve function can change over time, and some patients eventually need valve repair or replacement years or even decades later. Physical activity guidelines vary by individual, but most children with a good surgical result are not significantly restricted.