Conduction delay within the AV node, causing first or second degree and/or high grade AV block frequently accompanies an acute inferior wall myocardial infarction and is almost always transient. The frontal plane (limb) leads shown here are from an 83 year old female with an acute inferior wall infarction. There is complete AV block with AV dissociation and a narrow QRS complex escape rhythm, indicating that the site of block is within the AV node and that the escape pacemaker is located above the His bifurcation. Its rate is 44 beats per minute (R-R interval = 1.36 sec). The P waves are best seen in lead II (arrows). They have a normal configuration and a rate of 67 (P-P interval = 0.9 sec). The Q waves in leads II, III and aVF and the ST segment elevation in these leads reflect the acute inferior wall infarction.