Case presentation:

• Male.
• 3 months old.
• Admiitted because of cyanosis and hypoxemia, unmodified after oxygen therapy.
• Chest X-ray showed an opacity in the left upper field.

Teaching points:

• Pulmonary arterovenous fistulae may be multiple, and they may open at diferent ages.
• Perfusion lung scan allows a non-invasive, sensitive and reproducible quantification of right-to left-shunts, that correlates with hypoxemia.