PFO indicates there is a hole in heart wall that separates the right and left side of the heart chambers. That is a congenital defect and can vary in size and medical significance. The usual procedure is to give a bubble test. That test monitors the blood flow and if bubbles occur from one chamber to the other there is an opening.
It is medically significant when the shunt is from the right chamber to the left chamber because blood has not been to the lungs to be oxygenated and that contaminated blood goes into circulation and can cause hypoxia (heart cells less than normal oxygen) that will eventually cause a serious heart condition problem and there is a risk of stroke due to blood clots. The etiology, for example, would be clots that form in the lower peripherals break lose into the blood stream, and usually not a problem as the clots would go to the lungs and filtered before the blood goes to the left ventricle to pump blood into circulation. If there is right to left shunting the clot would get into the left ventricle and pumped into circulation having the potential to cause a stroke.
Usually there is not a right to left shunt because the intra chamber pressure is higher on the left side.
If there is double shunting, an option to correct would be considered. If the shunt is only left to right there may not be a problem that is significant. The information given is to provide an insight, and provide a perspective. You and your doctor would decide on whether or not to intervene with a procedure to correct.
Thanks for your questions and if you have any further questions or comments, you are welcome to respond. Take care,
Ken