In a first-degree heart block the PR interval is greater than 0.2 seconds with an otherwise normal rhythm. In a second-degree type I (Wenckebach) heart block, the PR interval progressively lengthens until the P wave is not followed by a QRS complex—the QRS has dropped off after the P wave. In a second-degree type II heart block (Mobitz II), conducted P waves can’t get through and may occur at random or in patterned ratios. In a third-degree heart block, none of the electrical impulses from the atria reach the ventricles, and the atria and ventricles beat independently. Remember these with the following poem:If the R is far from P, then you have a 1st degreeLonger, longer, longer, drop, then you have a WenckebachIf some Ps don’t get through, then you have a Mobitz IIIf Ps and Qs don’t agree, then you have a 3rd degree