A 73 year old woman with dizziness. 2 to 1 AV block (every other P wave is conducted to the ventricles) 2 to 1 AV block starts after the 5th QRS in this 3 channel recording. The first non-conducted P wave is indicated with an arrow. Note the long PR interval of conducted P waves is constant and the left bundle branch block 2 to 1 AV block cannot be classified into Mobitz type I or II as we do not know if the 2nd P wave would be conducted with the same or longer PR interval. with permision from the site of Dr. Dean Jenkins