Patients with patent ductus arteriosus may exhibit several clinical manifestations based on the amount of shunting. 1. Small shunt volume: The internal diameter of the patent ductus arteriosus is small, and the patient may exhibit no subjective symptoms. The prominent sign is a continuous machinery murmur heard at the left sternal border at the second intercostal space and below the left clavicle, accompanied by a thrill; pulse pressure may slightly increase. 2. Moderate shunt: Patients commonly experience fatigue, palpitations, shortness of breath, and chest discomfort after exertion. The heart murmur is similar in character to the above but louder, accompanied by a thrill, and widely transmitted. At times, diastolic and mild systolic murmurs caused by left ventricular enlargement, relative mitral valve insufficiency, and stenosis can be heard at the apex, with a positive vascular sign. 3. Large shunt volume: This condition in a patent ductus arteriosus often accompanies secondary severe pulmonary hypertension, leading to a right-to-left shunt. The typical murmur's diastolic component may diminish or disappear, followed by the disappearance of the systolic murmur, and only a diastolic murmur due to pulmonic valve insufficiency can be heard. Patients often exhibit cyanosis and severe clinical symptoms.