A 45-year-old lady with dyspnea and occasional precordial chest pain was diagnosed with a huge sinus venosus atrial septal defect and partial anomalous pulmonary venous return. Preoperative coronary angiography disclosed severe main stem stenosis, considered secondary to compression by the dilated pulmonary trunk. Atrial septal defect closure and pulmonary artery reduction plasty were performed. The left main coronary artery appeared completely patent. The postoperative course was uneventful, and the patient was asymptomatic on follow-up.