Depending on the size of the hole, most people with PFOs have no signs or symptoms. However, people with large holes(which is sometimes classified as a secundum atrial defect rather than a PFO) may experience some difficulties because of the volume of blood traveling from the right side of the heart to the left (right to left shunt), or vice versa, through the valve created by the septum primum.

These difficulties may include labored breathing, recurrent respiratory infections and other problems. Rarely, larger PFOs can lead to heart failure or even death. Depending on the size of the diameter of the opening, PFOs have also been associated with a greater risk of pulmonary embolism and stroke, although studies have recently shown that PFO is not linked to the occurrence of a second stroke, as was once suspected. Migraine headaches have also been linked to PFOs.

In many cases, patent foramen ovale (PFO) may be discovered when physicians are conducting tests for another cardiac problem, such as a heart murmur. The condition also may be suspected if an individual suffers a transient ischemic attack (TIA) or a stroke. However, PFO is not typical a cause of a cerebrovascular event.

Individuals with low blood oxygen levels also may be suspected of having PFO. This is especially true of patients with severe lung conditions, such as emphysema. Lung conditions can cause higher pressure on the right side of the heart. With the increased pressure, oxygen-poor blood to flows through the hole from the right side of the heart to the left side. This action further lowers oxygen levels in the blood and can lead physicians to suspect PFO.

To diagnose PFO, physicians may use the following tests:

• Transthoracic echocardiogram. This test uses sound waves (ultrasound) to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function.  This test does not involve radiation and is completely painless. No preparation is necessary prior to performing an echo. It may be done at the bedside.
  
  
• Transesophageal echocardiogram. This test uses a flexible tube similar to the endoscopes used to image the esophagus and stomach with a device that captures and records ultrasound images of the heart. It is a more sensitive test for detecting PFO and may be used in patients with an unexplained stroke. Additionally, this test can detect other cardiac conditions that may cause stroke.  This test requires some sedation and specialized monitoring.  It usually is only performed in specialized testing regions of a hospital.
  
  
• Transcranial doppler.  This is often done in conjunction with both the transthoracic and transesophageal echocardiogram.  A monitoring device is held against the side of the head over one of the arteries supplying the brain. A special liquid with extremely small bubbles is injected in a vein and the flow of this liquid through the heart is imaged. The tiny bubbles also will give a certain signal that can be picked up by the device held over the cerebral artery. This may help confirm the potential of a PFO to account for a stroke, TIA, or migraine headache.