This rhythm strip shows atrial tachycardia. The characteristic features demonstrated here include: a rapid, regular atrial rate between 180 and 240 beats per minute; and a constant P-R interval for those beats that are conducted. In this case, there is 2:1 A-V block with an atrial rate of 180 and the ventricle responding to every other P wave at a rate of 90. Atrial tachycardia with block is frequently due to digitalis intoxication.