Scimitar syndrome is an infrequent congenital malformation. It is a partial anomalous pulmonary venous drainage of the right lung into the inferior vena cava. Up to 25% of cases are associated with other heart diseases. The incidence in adults is reported to be 0.5-0.7%; classically, the adult form does not have pulmonary arterial hypertension, and may be unnoticed and asymptomatic for many years. It often presents after the second decade of life with nonspecific symptoms. Without surgical repair, clinical worsening, increased pulmonary pressure and sustained pulmonary arterial hypertension ultimately occur, when the syndrome is associated with other congenital heart diseases. We present the case of a 38-year-old woman diagnosed with scimitar syndrome associated with a large superior sinus venosus atrial septal defect, who underwent successful surgical repair using a lateral pericardial tunnel technique to redirect right pulmonary venous flow to the left atrium through a left atriotomy. This repair has shown good medium-term results. Possible complications such as tunnel thrombosis and stenosis will need to be explored in future assessments, and follow up must be lifelong.