Understanding Your Child's Diagnosis

Learning that your baby has a heart condition can feel overwhelming, but a Complete Atrioventricular Septal Defect (CAVSD) is a well-understood and highly treatable condition ^[1]. Most children who undergo surgery go on to live active, healthy lives ^[2].

Note: The treatment plan and its success depend heavily on whether your child’s heart chambers are evenly matched in size. We discuss this critical distinction in the next section.

What is CAVSD?

In a typically developing heart, walls (the septum) divide the heart into four chambers, and two separate valves control blood flow between the top and bottom sections. In CAVSD, the heart does not form these divisions correctly during the first few weeks of pregnancy ^[3][4].

The “center” of the heart fails to fuse together, resulting in:

• One large “hole”: Instead of two separate walls, there is one large opening in the center of the heart where the upper and lower chambers meet ^[5].
• A common valve: Instead of having two separate valves (mitral and tricuspid), there is one large common atrioventricular valve that sits over the hole ^[5].

Because of this structure, oxygen-rich blood and oxygen-poor blood mix together, and the heart has to work much harder to pump blood to the body ^[6].

The Link to Down Syndrome

There is a very strong connection between Down syndrome (Trisomy 21) and CAVSD. Approximately 20% to 40% of infants born with Down syndrome also have this specific heart defect ^[7][8].

While a diagnosis of both can feel like a lot to process, there is a silver lining regarding the heart: research shows that children with Down syndrome often have excellent results after CAVSD surgery ^[1][9]. In fact, they may actually be less likely to need follow-up surgeries for valve leaks later in life compared to children without Down syndrome ^[10].

Signs and Symptoms to Watch For

Because the heart is working extra hard, babies with CAVSD often show signs of “working” to keep up. These symptoms usually appear within the first few weeks or months of life ^[6][11]:

• Fast breathing (Tachypnea): Your baby may breathe rapidly even when they are resting or sleeping ^[6].
• Feeding difficulties: Feeding is the most “athletic” thing a baby does. You might notice your baby gets tired quickly, takes frequent breaks, or sweats—especially on the forehead—while eating ^[6][11].
• Slow weight gain (Failure to Thrive): Because the baby is burning so many calories just to breathe and pump blood, they may not gain weight as quickly as expected ^[6][12].

Managing the Wait Before Surgery

If your baby is struggling with these symptoms, they are not left untreated while waiting for surgery. The medical team will actively manage your baby’s condition to help them grow big and strong enough for the operation:

1. Feeding Support: To combat poor weight gain, doctors often prescribe heavily fortified, high-calorie formulas or breast milk ^[12]. If your baby gets too tired to eat enough, the team may suggest a temporary NG tube (a small, soft tube that goes through the nose into the stomach). This is very common and ensures your baby gets the calories they need without burning energy ^[12].
2. Medications: Doctors may prescribe diuretics (water pills) to help the baby’s body get rid of extra fluid in the lungs, making breathing easier ^[13].
3. Infection Prevention: Babies with CAVSD, especially those with Down syndrome, are at a very high risk for severe respiratory complications if they catch a virus. Your doctor will likely recommend strict isolation (avoiding crowds) and prescribe Synagis (Palivizumab), a preventative monthly injection to protect against RSV (Respiratory Syncytial Virus).

The goal of this pre-surgical period is simply to keep your baby growing, comfortable, and healthy until the surgical team determines it is the optimal time to repair the heart ^[14].