AV block is common with focal atrial tachycardia. The P waves are regular, with usually different morphology than sinus; rates range from 100 to 250 per minute. Some P waves are not conducted, with the most common AV ratio being 2:1. The block may at times be variable, leading to an irregular pulse rate. When atrial tachycardia, particularly with block, is seen in patients on digoxin, toxicity must be considered. The following animation illustrates what we have just described.