This case report describes a 24-year-old woman with a secundum atrial septal defect (ASD) who underwent successful percutaneous ASD closure with significant improvement in symptoms and functional capacity. The patient presented with easy fatigue and shortness of breath on exertion for 10 years. Echocardiography revealed a large secundum ASD with moderate to severe tricuspid regurgitation, mild mitral regurgitation, mild pulmonary regurgitation, and dilatation of the right atrium and ventricle. Right heart catheterization confirmed a large left-to-right shunt and pulmonary hypertension. The patient underwent ASD closure with a Figulla Flex II device, resulting in immediate improvement of hemodynamics. Follow-up at 3 and 6 months demonstrated decreased right ventricular size, improved left ventricular function, and increased exercise caapacity. This case highlights the benefits of ASD closure in improving symptoms and cardiac function, even in patients with longstanding right ventricular dilation.