The fetal shunt that directly connects the right and left atria, allowing blood to bypass the nonfunctional lungs, is the:

1. The fetal lungs are nonfunctional before birth, so blood must be diverted away from the pulmonary circuit. 2. One shunt accomplishes this at the level of the heart's upper chambers. 3. This atrial-level shunt is called the foramen ovale. 4. It directly connects the right and left atria, distinct from the ductus arteriosus, which diverts blood at the level of the pulmonary artery and aorta. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 28 "Development and Inheritance", p.1339 §The Fetal Circulatory System_