Partial anomalous pulmonary venous connection is frequently found in any ASD(atrial septal defect) patients. These patients are usually symptomatic, therefore, easily diagnosed as just simple ASD. We experienced a case of a 37-year-old female patient with ASD in which the left upper pulmonary vein was connected to SVC by the left inominate vein. The patient was diagnosed as simple ASD previously. During cardiac catheterization, we found a meaningful oxygen saturation step up between the SVC and its upper portion. Angiogram confirmed PAPVC. The surgical correction of anastomosis of PAPVC with left atrial appendage and direct closure of ASD were done. The patient was discharged 15 days later.