[Atrial septal defect of the ostium secundum associated with incomplete left bundle branch block].

The ECG in Ostium Secundum Atrial Septal Defect (O.S. ASD) shows typically a pattern of incomplete right bundle branch block with right axis deviation and a 12 year old boy suspected of having O.S. ASD on the basis of x-ray and echocardiographic findings showed an ECG pattern of incomplete left bundle branch block. Physical examination and a phonocardiogram revealed a single second heart sound. An ECG recorded at age five showed a typical pattern consistent with O.S. ASD. The angiographic examination confirmed the suggested diagnosis. This is, to our knowledge, the first case of O.S. ASD with incomplete left bundle branch block. The conduction disorder may have abolished the fixed splitting of the second heart sound.