The ductus arteriosus, a tube connected between the descending aortic arch and the pulmonary artery, is dependent on the fetal circulatory system during fetal life, but functional closure of the ductus arteriosus begins 10-15 hours after birth. According to statistics, 88% of infants have their ducts closed within two months of birth and 98% have closed within 8 months. If the duct is still open at the age of 1 week, there is less chance of self-closing later on, leaving a channel between the aorta and the pulmonary artery, which is called the end ductus arteriosus. It is more common, accounting for 15% of all precardiac disease, and is more common in female children. Sometimes, the ductus arteriosus is a lifeline for survival in children with complex cyanotic heart disease in which the ductus arteriosus is coexisting with reduced pulmonary blood flow. This is beyond the scope of this topic. What are the risks of an unclosed ductus arteriosus? Whether the heart is in systole or diastole, the aortic pressure is higher than the pulmonary artery pressure. The abnormal blood flow continues to flow from the aorta to the pulmonary artery, which is commonly referred to by physicians as a left-to-right shunt, resulting in increased blood flow to the pulmonary circulation, causing dilatation of the pulmonary artery and its branches and a corresponding increase in blood flow back to the left atrium and left ventricle, increased diastolic load on the left atrium and ventricle, and dilatation of the ascending aorta. The size of the shunt flow depends on the thickness of the lumen of the unclosed arterial duct and the pressure step difference between the main-pulmonary artery. In advanced stages of pulmonary hypertension with existing obstructive pulmonary vascular disease and pulmonary artery pressure approaching or exceeding aortic pressure, a right-to-left shunt, right ventricular hypertrophy, cyanosis, and pestle toe may occur. Cyanosis is evident in the lower extremities because the level of the shunt is distal to the left subclavian artery of the descending aorta. This is where the timing of the procedure may be lost.