The goal of this clinical trial is to explore the safety and efficacy of the FreeFlow percutaneous atrial septal shunt for treatment of idiopathic pulmonary arterial hypertension. The main questions it aims to answer are:

• Is the FreeFlow percutaneous atrial septal shunt safe to use in patients with idiopathic pulmonary arterial hypertension?
• Does the FreeFlow percutaneous atrial septal shunt reduce all-cause mortality and readmission in patients with idiopathic pulmonary arterial hypertension, and how effective is it? Thirty subjects who met the inclusion and exclusion criteria were selected for selective implantation of FreeFlow percutaneous atrial septal shunts after balloon atrial septostomy.

Participants will:

• underwent balloon atrial septostomy and FreeFlow percutaneous atrial septal shunt implantation.
• will be followed up at 24 hours after shunt implantation or before discharge, 1 month, 3 months, 6 months and 12 months.

Inclusion Criteria:

• 18≤ age ≤70 years old, female or male;
• 10 mmHg≤ mean right atrial pressure (mRAP) ≤20 mmHg;
• The subjects had severe idiopathic pulmonary hypertension (mean pulmonary arterial pressure > 45 mmHg);
• WHO grade III or IV;
• NT-proBNP≥650 ng/L;
• The subjects were informed of the nature of the study and agreed to all the requirements for participating in the study. They signed the informed consent form and agreed to complete the follow-up and the examinations required for the follow-up.

Exclusion Criteria:

• Local or systemic sepsis or other acute infection;
• Severe coagulopathy;
• Allergy to nickel and/or titanium and/or nickel/titanium-based materials;
• Patients with contraindications to antiplatelet, coagulant or thrombotic therapy;
• Intolerance to contrast media;
• Have participated in other drug or device clinical trials during the same period;
• Glomerular filtration rate (GFR) < 50 mL/min;
• Patients with severe liver dysfunction (alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 3 times the upper limit of normal);
• The patient had malignant arrhythmia;
• The patient did not receive standardized drug therapy (triple sequential therapy) according to the Chinese guidelines for the diagnosis and treatment of pulmonary hypertension within 3 months;
• Women who are pregnant, planning to become pregnant (within 12 months) or breastfeeding;
• Severe restrictive or obstructive lung disease;
• Implanted atrial septal defect (ASD)/ patent foramen ovale (PFO) closure device;
• Left ventricular ejection fraction (LVEF) <50%;
• SpO2 < 90% without oxygen inhalation (pulse measurement);
• The anatomical structure of the heart is abnormal, and the shunt cannot be implanted on the atrial septum;
• Other circumstances in which the patient was deemed by the investigator to be ineligible for inclusion in the trial.