It is important to diagnose AV-blocks precisely because unnecessary pacemaker placement in patients with pseudo-AV blocks can worsen symptoms and create complications.

In a second-degree AV block, the impairment results in a failure to conduct an impulse, which causes a skipped beat.

[5] Mobitz II is caused by a sudden, unexpected failure of the His-Purkinje cells to conduct the electrical impulse.

Persons with third-degree AV block need emergency treatment including but not limited to a pacemaker.

[8] There are many causes of AV block, ranging from a normal variant among people to the result of a heart attack.

[9] It is also possible that a high degree block can result after cardiac surgery during which the surgeon was in close proximity to the electrical conduction system and accidentally injured it.

Reversible causes of Mobitz II and third-degree heart block include untreated Lyme disease, hypothyroidism, hyperkalemia (high levels of potassium), and drug toxicity.

Drugs that slow the conduction of the electrical signal through AV node, such as beta-blockers, digoxin, calcium channel blockers, and amiodarone, can cause heart block if they are taken in excessive amounts, or the levels in the blood get too high.

[citation needed] The electrical signal then travels to the AV node located on the lower portion of the interatrial septum.

[13] Based upon clinical suspicion, the physician may do lab tests to assess for reversible causes of AV block, such as hypothyroidism, rheumatologic disorders, and infections (such as Lyme disease).

[12] Management is dependent upon the severity, or degree, of the blockage, the consistency of symptoms, as well as the cause of the AV block.

[9] Patients with first-degree AV block do not have any resulting severe or life-threatening symptoms, such as symptomatic bradycardia or hypotension, and, thus, do not require treatment.

[5] Patients with second-degree Mobitz II and third-degree heart block are much more likely to have symptomatic bradycardia and hemodynamic instability, such as hypotension.