Patent foramen ovale UMLS:C0016522 PFO HP:0001655 Fyler:2020 Failure of the foramen ovale to seal postnatally, leaving a potential conduit between the left and right cardiac atria. ICD-10:Q21.1 The foramen ovale is located in the atrial septum and is essential for proper fetal circulation. With separation from the placenta and with the first few breaths, the left atrium fills with blood returning from the lungs and closes the foramen ovale. Subsequently, during the first years of life, the foramen ovale seals shut. SNOMEDCT_US:204317008 Persistent foramen ovale Abnormal cardiac septum morphology