Pulmonary artery aneurysm (PAA) and pulmonary artery dissection (PAD) are rare and potentially fatal conditions that may lead to pulmonary artery (PA) rupture and cardiac tamponade. PAA is often associated with other cardiac and congenital heart diseases, such as atrial septal defect (ASD). We report a case of a patient with ASD and a giant dissecting PAA who underwent surgical repair to prevent potentially fatal outcome and discuss the probable etiologies of this case. We present a rare case of a 50-year-old woman with a secundum ASD and severe pulmonary arterial hypertension (PAH) who developed a giant PAA of 114 mm with dissection. The PAA caused extrinsic compression of the left main coronary artery (LMCA), which was misdiagnosed as coronary artery disease (CAD) at local hospital. Right heart catheterization revealed PAH of 73 mmHg and she was referred to our center for further treatment. After 4 months of lowering PAH treatment, she underwent successful surgical repair of the PAA to release the compression of LMCA, as well as mechanical valve replacement, fenestrated ASD closure and tricuspid valvuloplasty. She had an uneventful recovery and showed significant improvement in pulmonary hemodynamics and clinical symptoms at one-year follow-up. PAA with dissection is a rare complication of ASD and PAH that can potentially be fatal. Patients with large or symptomatic PAA and PAD may require early surgical intervention, particularly if they experience compression of nearby structures or are at risk of rupture. It is crucial to promptly refer and consult with specialists and ensure optimal preoperative hemodynamic management to enhance patient outcomes.