As mentioned above (page 3.3.6), the ECG associated with an ostium primum atrial septal defect most frequently reveals the combination of right bundle branch block and left anterior fascicular block. This ECG is from a 3 year old child with that form of congenital heart disease and shows the characteristic findings of right bundle branch block with left anterior fascicular block. As in the previous tracing, try to determine the frontal plane axis of the initial, middle and terminal parts of the QRS complex. Then project the spatial vectors of these components in the frontal plane as on pages 3.3.11 and 3.3.12 and draw the loop that encompasses them.