In patients receiving digitalis, the development of an ectopic atrial tachycardia with 2:1 AV block, as in the example shown here, is usually a manifestation of digitalis excess and the site of block is within the AV node. This tracing was shown in the previous chapter (page 7.2.30). The rate of the ectopic atrial tachycardia is 214 (PP = 0.28 seconds) and there is 2:1 AV conduction. The ectopic P waves are best seen in lead V1 (arrows).