Right atrial enlargement on chest radiography (illustration)

The right atrial shadow (convexity in the lower half of the right mediastinal cardiovascular border) is usually:

• not more than 50% of the cardiovascular height
• not more than 5.5 cm from the midline

A markedly enlarged right atrium results to:

• elongation of the right heart border (length of right atrial convexity exceeds 50% of the mediastinal cardiovascular shadow)
• lateral bulging of the right heart border (right atrial margin is more than 5.5 cm from the midline)