Left main coronary artery compression by dilated pulmonary artery in patients with atrial septal defect has previously been reported, but not well characterized. Accordingly, we review retrospectively data of patients with atrial septal defect in whom selective coronary angiograms were done. 41 patients (26 females), aged 47.3 +/- 7.4 years were studied. The pulmonary artery mean pressure was 22.7 +/- 8.3 mm Hg and all patients had left to right shunt ratio of 2:1 or more (mean ratio: 3.9 +/- 1.7). Two patients (4.8%) had left coronary ostial stenosis. There were no clinical or haemodynamic parameters to differentiate the patients with or without these changes. Two patients (4.8%) had coexistent atherosclerotic coronary artery disease. In conclusion, left main coronary trunk compression rarely occurs in patients with atrial septal defect. This information may be relevant in evaluating patients with atrial septal defect.