Third-degree heart block, also referred to as third-degree atrioventricular (AV) block or complete heart block, is a disorder of the cardiac conduction system with complete absence of AV conduction. No P waves conduct to the ventricle, and AV dissociation is complete.

Establish secure large-bore intravenous access.
Withhold AV nodal agents and deliver anti-ischemic therapy where appropriate.
Apply and test transcutaneous pacing patches for all patients with third-degree heart block.
Hemodynamically stable patients in whom pacing can be established transcutaneously can be admitted to a telemetry unit. They may undergo elective placement of a permanent pacemaker at the discretion of the cardiologist.

Symptomatic patients and those in whom transcutaneous pacing is tested unsuccessfully should have urgent cardiac consultation for the placement of a temporary transvenous pacing wire.
Hemodynamically unstable patients may be treated with atropine, although this will be ineffective in patients with a wide complex escape rhythm. Use caution in administering atropine in the setting of a suspected acute MI, as the resulting vagolysis leads to unopposed sympathetic stimulation, causing increased ventricular irritability and, potentially, ventricular tachycardia (VT)/ventricular fibrillation (VF).
Hemodynamically unstable patients for whom timely cardiology consultation is unavailable should undergo temporary transvenous pacemaker insertion in the ED by the ED physician.