In patients with patent ductus arteriosus, since the aortic pressure is significantly higher than the pulmonary artery pressure throughout the cardiac cycle, there is continuous blood flow from the aorta into the pulmonary artery through the open duct, causing a left-to-right shunt. This increases the blood volume in the pulmonary circulation, causing dilatation of the pulmonary artery and its branches. The blood flow returning to the left heart system also increases, thereby increasing the load on the left heart and causing the left heart to enlarge. Due to the diastolic diversion of blood from the aorta to the pulmonary artery, the peripheral arterial diastolic pressure decreases and the pulse pressure increases.