A hole in the heart is a literal opening in the wall of tissue (the septum) that separates the heart’s chambers. It can range from a tiny pinprick smaller than a toothpick’s width to a gap the size of a pea or larger. Most are present from birth, and how they look depends on where they form, how big they are, and whether they’re a true hole or more of a flap that didn’t seal properly.
Where the Hole Forms
Your heart has four chambers: two upper ones (atria) and two lower ones (ventricles). A wall of muscle and tissue runs down the middle, keeping oxygen-rich blood on the left side separate from oxygen-poor blood on the right. A hole in the heart is a gap in that wall, and it gets a different name depending on its location.
An atrial septal defect (ASD) is a hole in the wall between the two upper chambers. It can appear in different spots along that wall. The most common type sits right in the center of the dividing wall. Others open near the bottom, close to the heart’s internal valves, or near the top where large veins enter the heart.
A ventricular septal defect (VSD) is a hole in the thicker, more muscular wall between the two lower chambers. VSDs are the most common congenital heart defect overall. Because the lower chambers do the heavy pumping, even a moderate-sized hole here can create significant problems.
True Holes vs. Unsealed Flaps
Not every opening in the heart looks the same. A true ASD or VSD is an actual gap in the tissue, like a hole punched through a sheet of muscle. But another common finding, called a patent foramen ovale (PFO), looks quite different. Before birth, every baby has a small opening between the upper chambers that allows blood to bypass the lungs (which aren’t yet in use). After birth, a flap of tissue normally seals this passage shut.
In roughly one in four adults, that flap never fully fuses. A PFO appears on imaging as a slit or tunnel-like passage rather than a round hole. It functions like a one-way door: under certain conditions (coughing, straining), the flap can briefly open and let a small amount of blood cross over. The tissue overlap sometimes becomes so loose it balloons out, creating a bulging pouch in the septum. In borderline cases, distinguishing a PFO from a small ASD can be difficult even for specialists.
How Big These Holes Actually Are
Size is the single biggest factor in whether a hole causes problems. VSDs are classified in three tiers. A small hole is less than 3 millimeters across, roughly the diameter of a toothpick tip. Most people with holes this size never develop symptoms, and many of these defects close on their own during childhood. A moderate hole measures 3 to 5 millimeters. A large hole ranges from 6 to 10 millimeters, about the size of a pea. At that size, enough blood leaks between chambers to strain the heart.
ASDs tend to be somewhat larger at diagnosis because they often go undetected longer. A small ASD may measure under 5 millimeters, while a large one can exceed 2 centimeters, roughly the width of a nickel.
What Happens Inside the Heart
When a hole is present, blood follows the path of least resistance. Because the left side of the heart pumps at higher pressure than the right, blood typically leaks from left to right through the opening. This is called a left-to-right shunt. The result is that the right side of the heart and the lungs receive more blood than they should, while the rest of the body gets less.
Over time, a large shunt forces the right side of the heart to work harder and can permanently damage the blood vessels in the lungs. If pressure on the right side eventually exceeds the left, the shunt reverses direction. Blood that hasn’t picked up oxygen starts flowing into the body’s circulation. This reversal, known as Eisenmenger syndrome, occurs in roughly 10 to 15 percent of people with unrepaired VSDs and represents the most serious long-term consequence of a large hole.
What You Might See on the Outside
A small hole in the heart produces no visible signs at all. Many adults live decades without knowing they have one. Larger defects, especially those that allow oxygen-poor blood to reach the body, can cause a bluish or purple tint to the skin, lips, and nail beds. This discoloration, called cyanosis, is often the first visible clue in newborns with significant heart defects. In babies, the blue tint is most noticeable around the mouth and fingertips.
How Doctors See the Hole
The primary tool for visualizing a hole in the heart is an echocardiogram, essentially an ultrasound of the heart. On the screen, a normal septum appears as a solid, continuous band of tissue. When a defect is present, the wall shows a visible gap or “dropout” where tissue is missing.
Doctors then add color Doppler imaging, which overlays the echocardiogram with color-coded blood flow. Blood moving toward the ultrasound probe appears red, and blood moving away appears blue. A hole shows up as a jet of color streaming through the septum where no flow should exist. This color jet makes even small defects easy to spot and helps measure how much blood is crossing over. The imaging also reveals the exact position of the hole, the length of tissue rim surrounding it, and whether the heart chambers have enlarged from the extra workload.
What a Closure Device Looks Like
When a hole needs to be closed without open-heart surgery, doctors can thread a small device through a blood vessel and position it inside the heart. The most widely used design consists of two flat discs connected by a short waist, resembling a tiny dumbbell or cufflink. One disc sits on the left side of the septum and the other on the right, sandwiching the hole between them.
On imaging after the procedure, a properly placed device appears as a flat, disc-shaped structure straddling the septum with its waist snugly filling the defect. If the device is too large for the hole, the waist bunches up and the whole thing takes on a mushroom shape rather than lying flat. Doctors check for this on follow-up scans to make sure the closure is secure and no blood is still leaking around the edges.
How Common These Defects Are
Congenital heart defects affect roughly 9 out of every 1,000 babies born today, up from about 4.5 per 1,000 in the early 1970s. That increase is largely driven by better detection of mild defects rather than a true rise in heart abnormalities. ASD diagnoses have increased six-fold over that period, and VSD diagnoses have doubled to tripled, mostly because modern ultrasound catches holes that would have gone unnoticed a generation ago. Many of these small defects close on their own or never require treatment.