This example of complete AV block is from a 78 year old female who was receiving digitalis for treatment of congestive heart failure. The tracing shows sinus P waves with a rate of 70 that are dissociated from the QRS complexes. The QRS complexes, themselves, have a slower rate and are of normal duration, indicating that as in the previous tracing, their site of origin is above the His bundle bifurcation. In this patient, the block was most probably caused by the digitalis and the site of block was most likely within the AV node.