The foramen ovale is a small opening in the heart that exists in the fetal stage. It allows blood to flow directly from the right atrium to the left atrium, bypassing the lungs, which are not yet functioning. This is crucial for fetal development, as the fetus receives oxygen through the placenta rather than its lungs. After birth, the foramen ovale typically closes as the pressure in the left atrium increases, allowing normal blood flow to the lungs. If it remains open, a condition known as patent foramen ovale (PFO) can occur, which may lead to complications such as stroke or other cardiovascular issues.