A hole in the heart is most often something you’re born with. It forms during the first four to seven weeks of pregnancy, when the walls separating the heart’s chambers don’t fully develop or close. About 1 in 100 babies are born with some type of structural heart defect, and holes in the dividing walls are among the most common. Less often, a hole can develop later in life after a heart attack damages the muscle wall between chambers.
Types of Heart Holes
The heart has four chambers, and the walls between them (called septa) are supposed to keep oxygen-rich blood separate from oxygen-poor blood. A hole can appear in different locations, and each type behaves differently.
An atrial septal defect (ASD) is a hole between the two upper chambers. These are present at birth. Small ones sometimes close on their own during childhood, but larger ones can persist and gradually strain the heart by letting blood flow back toward the lungs instead of out to the body.
A ventricular septal defect (VSD) is a hole between the two lower chambers, the heart’s main pumping rooms. VSDs are the most common congenital heart defect. Because the lower chambers generate more pressure than the upper ones, even a moderate VSD can push a significant volume of blood in the wrong direction.
A patent foramen ovale (PFO) is a special case. Every baby has a small flap-like opening between the upper chambers before birth, which normally seals shut shortly after delivery. In roughly 25% of adults, it never fully closes. Most people with a PFO never know they have one and never need treatment, though it can occasionally be linked to stroke in younger adults when a small blood clot crosses through the opening.
How the Heart Forms During Pregnancy
The heart is the first organ to function in a developing embryo, and its internal walls take shape between weeks four and seven of pregnancy. During this window, sheets of tissue grow inward from multiple directions and must meet, overlap, and fuse precisely to create separate chambers. Specialized cells called neural crest cells migrate into the developing heart to help sculpt the walls of the outflow tracts, the pathways that become the aorta and pulmonary artery.
The wall between the upper chambers forms in layers. A tissue flap grows downward, and a ridge of tissue called the atrial spine expands across the center of the heart. These structures must merge with cushion-like pads in the middle of the heart by the end of the sixth week. If the atrial spine doesn’t develop properly, the opening between the upper chambers stays open, resulting in an ASD. The wall between the lower chambers follows a similar process, with muscular tissue growing upward and fibrous tissue filling the remaining gap. If any step in this sequence is incomplete, a VSD remains.
Because so many structures must align within just a few weeks, even minor disruptions to cell signaling or blood flow during this period can leave a hole behind.
Genetic Causes and Chromosomal Conditions
Certain genetic conditions dramatically raise the odds of being born with a heart hole. Down syndrome (trisomy 21) is the most widely recognized, but it’s far from the only one.
- Noonan syndrome involves heart abnormalities in 80% to 90% of affected individuals, including ASDs and a type of defect where the walls between both upper and lower chambers are incomplete.
- Holt-Oram syndrome causes hand and arm bone abnormalities alongside heart defects. About three-quarters of patients have ASDs, VSDs, or both.
- DiGeorge syndrome (22q11 deletion) is associated with a range of complex heart defects, including VSDs and ASDs.
- Trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) both carry high rates of ASDs and VSDs along with other structural heart problems.
- Alagille syndrome produces cardiovascular abnormalities in over 90% of cases, including septal defects.
A heart hole can also occur without any identifiable syndrome. In many cases, it results from small variations across multiple genes rather than a single dramatic mutation, which is why most babies born with a heart hole have no family history of heart defects.
Environmental Factors During Pregnancy
What happens in the mother’s body during those critical first weeks of heart development matters as much as genetics. Several well-documented environmental exposures increase risk.
Maternal diabetes, particularly diabetes that existed before pregnancy, is one of the strongest risk factors. It appears to interfere with heart formation before the seventh week of gestation, the exact window when the chamber walls are taking shape. Associated defects include VSDs, outflow tract abnormalities, and complex structural problems.
Rubella infection during early pregnancy can cause a group of heart defects including VSDs and problems with the pulmonary valve. Widespread vaccination has made rubella-related heart defects rare in many countries, but they still occur in regions with lower immunization rates.
Certain medications pose risks when taken during early pregnancy. Thalidomide, now used for specific cancers and inflammatory conditions, causes heart defects ranging from simple ASDs and VSDs to complex structural problems. Isotretinoin, a powerful acne medication, is a known cause of heart and great vessel defects. Some anti-seizure medications, including phenytoin and valproic acid, have been linked to congenital heart defects, though researchers have found it difficult to separate the effect of the medication from the effect of the seizure disorder itself.
Heart Holes Caused by a Heart Attack
Not every heart hole is present from birth. A heart attack can, in rare cases, tear a hole through the wall between the lower chambers. This is called a ventricular septal rupture, and it happens when a blockage cuts off blood supply to the muscle of the dividing wall. The septum between the ventricles is fed by small branches of the major coronary arteries. When those branches are blocked, the tissue dies, weakens, and can tear apart. The force of the still-healthy surrounding muscle contracting against the damaged zone makes the tear worse.
Ventricular septal rupture is a medical emergency. Unlike a congenital VSD that the body may have adapted to over years, a sudden hole between the ventricles causes an abrupt drop in the heart’s ability to pump blood to the body, because a large portion of each heartbeat now flows backward into the lungs.
What a Heart Hole Does to Blood Flow
To understand why heart holes matter, it helps to know what goes wrong with circulation. Normally, the left side of the heart pumps oxygen-rich blood to your body, and the right side pumps oxygen-poor blood to your lungs. A hole between the two sides creates a shortcut.
Because pressure is higher on the left side, blood typically flows from left to right through the hole. This means oxygen-rich blood that should be heading to your organs instead loops back to the lungs. The lungs and the right side of the heart end up handling more blood than they’re designed for. A small hole may cause no noticeable symptoms for decades. A larger one gradually overworks the right side of the heart and raises pressure in the lung arteries.
With a VSD specifically, the high pressure of the left ventricle can transmit directly into the lung arteries, something that doesn’t happen with an ASD because the upper chambers generate much less force. Over time, if a large VSD goes unrepaired, the blood vessels in the lungs respond to this chronic pressure overload by thickening their walls. As those vessels narrow, resistance in the lungs rises until it eventually exceeds the resistance in the rest of the body. At that point, blood flow through the hole reverses direction, sending oxygen-poor blood out to the body. This condition, called Eisenmenger syndrome, represents permanent damage to the lung vasculature and is the main reason large heart holes are repaired early in life rather than watched indefinitely.
When Repair Is Needed
Small holes often close on their own during childhood or remain so minor they never cause symptoms. A PFO that isn’t associated with stroke or other complications typically requires no treatment at all.
Larger ASDs and VSDs that cause the right side of the heart to enlarge, or that produce symptoms like shortness of breath or poor growth in children, generally need to be closed. Many ASDs can now be closed without open-heart surgery using a catheter-based procedure, where a small device is threaded through a vein and expanded across the hole. The edges of the hole need enough surrounding tissue to anchor the device securely. If the hole is too large or in an awkward location, surgical repair through the chest is the alternative.
VSDs that don’t close on their own and are large enough to affect heart function are typically repaired surgically, often in the first year of life. The goal with any repair is to correct blood flow before the lungs sustain permanent pressure damage. Once Eisenmenger syndrome develops, closing the hole is no longer an option because the right side of the heart has become dependent on the hole as a pressure release valve.