Diagnosis is based on echocardiography. The defect may go unnoticed without careful examination. If an ASD is identified, a thorough search for other cardiac anomalies is warranted. Contrast echocardiography and DE are useful aids. Care should be taken not to interpret artefactual drop-out of the atrial septum as a defect. A characteristic 'T sign' with apparent increased echogenicity of the septum either side of the hole is usually seen with real defects (Figure 5.5).