This ECG is from a 49 year old asymptomatic patient with a large atrial septal defect and right ventricular dilatation but without an increase in pulmonary artery pressure. It shows normal sinus rhythm and complete right bundle branch block with a QRS duration of 120 ms (0.12 sec). Note that the main frontal plane QRS axis is normal and that there are no changes to suggest right ventricular hypertrophy.