Patent foramen ovale (PFO) is a hole between your heart's upper chambers. A test called an echocardiogram is used to diagnose a PFO.The test uses sound waves to create pictures of the beating heart. A patent foramen ovale (PFO) is a hole in the wall that that separates the heart's two upper chambers (atria). Learn more from Boston Children's Hospital. The foramen ovale is a hole in the wall between the left and right atria of every human fetus. This hole allows blood to bypass the fetal lungs. A patent foramen ovale (PFO) is a hole in the heart that didn't close the way it should after birth. We are experts in identifying the symptoms and causes of patent foramen ovale, and can perform any of the required diagnostic and catheter-based procedures. A patent foramen ovale (PFO) is a small opening between the two upper chambers of the heart, the right and the left atrium.