Yes, every baby is born with a small opening between the upper chambers of the heart. This hole, called the foramen ovale, is a normal and essential part of fetal development. It allows blood to bypass the lungs, which don’t function until a baby takes its first breath. In most people, the hole closes on its own shortly after birth. But in roughly 1 in 4 adults, it never fully seals.
Why Babies Need This Opening
Before birth, a baby gets all its oxygen from the placenta, not from breathing. Because the lungs aren’t doing any work yet, there’s no reason to pump large volumes of blood through them. The fetal circulatory system uses small passages called shunts to route blood around organs that aren’t fully online, particularly the lungs and liver.
The foramen ovale is one of these shunts. It sits in the wall (septum) between the heart’s two upper chambers. When blood enters the right atrium, most of it flows directly through this opening into the left atrium, skipping the lungs entirely. From there, it moves into the left ventricle and out through the aorta to supply the rest of the body. This is an elegant workaround: the baby gets oxygen-rich blood from the placenta distributed efficiently without wasting effort on organs that aren’t ready.
What Happens After Birth
The moment a newborn takes its first breath, pressure changes inside the heart cause the foramen ovale to functionally close. The tissue on either side of the opening presses together like a flap. Over the following weeks and months, this tissue grows together permanently, sealing the hole and leaving a small indentation on the septum wall. Once sealed, blood follows the route you’d expect: the right side of the heart pumps blood to the lungs for oxygen, and the left side sends that freshly oxygenated blood out to the body.
When the Hole Doesn’t Close
In about 25% of people, the flap never fuses completely. This is called a patent foramen ovale, or PFO. “Patent” simply means “open.” A PFO is not a birth defect. It’s the normal fetal opening that just didn’t finish closing. Most people with a PFO have no symptoms, never know about it, and live completely normal lives. PFOs are typically discovered by accident during tests for unrelated health problems.
A PFO is different from an atrial septal defect (ASD), which is a true congenital heart defect. An ASD is a hole in the septum that was never supposed to be there, often larger and more likely to cause problems. A PFO, by contrast, is simply leftover anatomy from fetal life.
Potential Risks of an Unclosed PFO
For the vast majority of people, a PFO causes no complications. In rare cases, though, it can create a pathway for trouble. The most significant concern is stroke. Normally, small blood clots that form in veins travel to the right side of the heart and get filtered out in the lungs. If there’s an open PFO, a clot can slip through the gap into the left atrium, reach the brain, and block blood flow. This is called a paradoxical embolism.
When someone has a stroke with no identifiable cause (known as a cryptogenic stroke), doctors often look for a PFO. Research has found that people with cryptogenic strokes are about three times more likely to have a PFO than people without strokes. In rare cases, a PFO can also allow enough blood to bypass the lungs that oxygen levels drop slightly, though this is uncommon.
How a PFO Is Found
Since PFOs rarely produce symptoms, they’re usually detected through an echocardiogram, an ultrasound of the heart. A standard echocardiogram uses a probe pressed against the chest to create moving images of the heart’s structure and blood flow. Color Doppler imaging can show the speed and direction of blood moving through the chambers, which helps identify abnormal flow patterns through a gap in the septum.
The most definitive test is a bubble study. During an echocardiogram, a small amount of sterile saline containing tiny air bubbles is injected into a vein. The bubbles travel to the right side of the heart and are normally filtered out by the lungs. If bubbles appear on the left side of the heart, it means they crossed through an opening in the septum, confirming a PFO.
When Treatment Is Considered
Most PFOs need no treatment at all. Closure is typically only considered in specific situations, most commonly when a PFO has been linked to a stroke or when it causes low blood oxygen levels (oxygen saturation below 90% at rest or during physical activity). The closure procedure is usually done with a small device threaded through a vein to the heart, where it plugs the opening. For someone with a PFO and no associated problems, the standard approach is simply to leave it alone.
So while it’s true that every human starts life with a hole in their heart, this is by design. It’s a feature of fetal circulation, not a flaw. And even when the hole sticks around into adulthood, it’s overwhelmingly harmless.