Introduction: Atrial Septal Defect (ASD) is the commonest adult congenital heart defect. 15% of these patients will eventually develop pulmonary hypertension (PHTN) if left untreated. Moreover, some cases will present when PHTN has ensued or has even become systemic, reducing their chances for successful closure. Partial ASD closure has been reported in the elderly and in cases of severe PHTN, with variable results. In this report we describe our experience with closing of a moderate-to-large symptomatic ostium secundum ASD associated with severe PHTN in a 52 year old male in NYHA class III with no other clinically meaningful treatment alternatives. Methods: TEE confirmed a secundum ASD of 26 mm, volume overload of right heart and bidirectional shunt. Hemodynamic study at room air and with O2 10 L/ min showed: left -to-right shunt (QP/QS: 1.7), sPAP = 90 mm Hg, systolic Ao pressure = 120 mmHg, PVR = 7.84 WU. The patient was denied surgical correction. We decided to perform endovascular closure with a dedicated device. The defect was partially closed using a fenestrated Occlutech Figulla Flex II ASD device under general anesthesia and TEE guidance. The occluder consisted of a Nitinol-wire mesh with “shape-memory”. Two patches of PET ensure faster sealing of the defect whilst optimizing tissue ingrowth. Th e left atrial disc = 42 mm, the right atrial disc = 38 mm and a waist = 27 mm; a para-central fenestration of 6 mm was created by the manufacturer. Results: The implantation procedure was successful without any complication. The patient received heparin 100 IU/kg during the procedure and kept on dual oral antiplatelet therapy (aspirin and clopidogrel) for the 6 months. Antimicrobial prophylaxis against infective endocarditis was also recommended. Post-procedure and 1 month TTE confirmed that the fenestration is still patent and estimated systolic pulmonary artery pressure dropped from 90 mmHg to 35 mm Hg, right ventricular diastolic dimensions slightly decreasing. Immediate marked symptomatic improvement was obtained. No device malfunction or thrombus formation was detected so far. We plan for definitive closure of the fenestration with an appropriate second ASD Occluder in the near future, as far as PA pressure remains normal. Conclusions: Management of large secundum ASD and severe PHTN has proven to be challenging. Partial closure is a safe and feasible treatment option to reduce the magnitude of the shunt when using a custom made fenestrated device. Long term follow up is imperative to plan second stage closure of the fenestration.