Patent ductus arteriosus (PDA) is a heart defect found in the days or weeks after birth. The ductus arteriosus is a normal part of fetal blood circulation.The foramen ovale is a hole in the wall between the left and right atria of every human fetus. This hole allows blood to bypass the fetal lungs. Patent ductus arteriosus (PDA) is a condition in which the ductus arteriosus does not close. The word "patent" means open. The purpose of this guide is to provide you with basic information about filing a utility patent application with the USPTO. Causes of Bilateral Foraminal Stenosis. When the pulmonary valve is blocked (obstructed), the right ventricle must work harder to push blood into the pulmonary artery. The pulmonary stenosis and right ventricular outflow tract obstruction seen with tetralogy of Fallot usually limits blood flow to the lungs.