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 important for fetal circulation, as the fetus receives oxygenated blood from the mother through the placenta. After birth, the foramen ovale usually closes as the lungs become functional and blood flow changes. If it remains open, a condition known as patent foramen ovale (PFO) can occur, which may lead to complications such as blood clots traveling to the brain, potentially causing a stroke.