Break the fossa ovalis and you break the heart. The heart is a binary form with two distinct sides: oxygen-free blood moves into the right atrium, then out again to the lungs where it is oxygenated and returns through the left atrium. In the fetal heart the foramen ovale is an opening between the left and right atrium that seals at birth. A fetus, not yet individuated from the mother, receives oxygen from the placenta rather than the lungs, so oxygenated blood must travel directly between the atriums through a flap called the septum primum. When a baby is born its first breath pushes the septum primum against the atrial septum, closing the forman; the remaining depression is the fossa ovalis. Rare cases in which the seal is not complete can lead to decompression sickness, paradoxical embolism, migraine, possibly even stroke and transient ischemia attacks. But before now there has never been a reported case of the fossa ovalis reopening. The cause is unknown but the effect is fatal. The heart cannot support this unregulated flow and is engorged until it erupts, causing the inflated chest cavities and withered extremities that characterize this brutal death. There is no known cure.