Cor triatriatum sinister is a rare congenital anomaly characterized by the left-sided triatrial form of the heart. Diverse theories have been proposed regarding its formation, and the failure of incorporation of the common pulmonary vein into the left atrium (LA) during embryogenesis is the most widely accepted theory. Accordingly, cor triatriatum sinister may be associated with pulmonary venous obstruction and post-capillary pulmonary hypertension in the setting of restricted fenestration. A high proportion of patients with cor triatriatum sinister also have an associated secundum atrial septal defect. Pre-capillary pulmonary hypertension, which is unusual in patients with small atrial septal defects (<2 cm), is probably not as rare as some reports indicate, especially when combined with complex comorbidities. The conventional treatment strategy of atrial septal defect closure in patients with pulmonary hypertension, whether associated with cor triatriatum sinister or co-existing multiple cardiac anomalies, involves simultaneous repair with other cardiac surgical procedures. To the best of our knowledge, there is no reported clinical experience of percutaneous atrial septal defect closure in the literature. Herein, we present the case of an elderly female with pulmonary hypertension and coexisting cor triatriatum sinister, secundum atrial septal defect, and multiple cardiac anomalies. Despite optimal medical therapy, the biventricular failure deteriorated, and clinical stabilization could not be achieved. Transcutaneous atrial septal defect closure was then performed. Subsequent investigations showed an initial improvement (perhaps due to elimination of the left-to-right shunt) from this intervention, but the long-term impact did not appear favorable, likely due to multiple uncorrected cardiac anomalies. To the best of our knowledge, this is the first clinical report showing that partial treatment of combined pre- and post-capillary pulmonary hypertension by eliminating the pre-capillary component may have an initial benefit; thus, total surgical correction should be considered a definite therapeutic strategy unless contraindicated.