An unclosed ductus arteriosus can cause an increase in blood volume in the pulmonary circulation, which in turn increases the volume of the left ventricle and the ejection of blood from the heart, causing both systolic and diastolic arterial pressure to rise, but the systolic increase is greater than the diastolic increase, leading to an increase in the pulse pressure difference. When the arterial conduit is not closed, blood from the aortic arch enters the pulmonary artery through the unclosed arterial conduit, causing an increase in blood volume in the pulmonary circulation. The long-term increase in pulmonary blood leads to an increase in the volume of blood entering the left atrium and the left ventricle through the pulmonary vein, an increase in cardiac preload, and an increase in the volume of beat-to-beat, which causes an increase in the arterial wall pressure. However, systolic blood pressure rises more than diastolic blood pressure, resulting in a greater difference in pulse pressures. In the fetal period, the ductus arteriosus is an important blood vessel connecting the main pulmonary artery to the aorta, and it normally closes automatically within 72 hours after birth. Failure to close it completely will result in ductus arteriosus insufficiency, which often occurs in preterm infants, especially those with respiratory distress syndrome. Therefore, preterm infants should have a cardiac ultrasound after birth to detect problems early.