This ECG shows Mobitz type I second-degree AV block, also known as Wenckebachphenomenon, characterized by progressive PR interval prolongation prior to block of an atrial impulse. This rhythm generally does not require therapy. It may be seen in normal individuals; other causes include inferior MI and drug intoxications such as from digoxin, beta blockers, or calcium channel blockers. Even in the post-MI setting, it is usually stable, although it has the potential to progress to higher-degree AV block with consequent need for pacemaker.