First-degree atrioventricular block (AV block) is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node (AV node) more slowly than normal.

These include calcium channel blockers, beta-blockers, cardiac glycosides, and anything that increases cholinergic activity such as cholinesterase inhibitors.

[3] In first-degree heart block, the AV node conducts the electrical activity more slowly.

[4] First-degree heart block does not require any particular investigations except for electrolyte and drug screens, especially if an overdose is suspected.

If this is not feasible, clinicians should be very cautious when introducing any drug that may slow conduction; and regular monitoring of the ECG is indicated.

In the Framingham Heart Study, however, the presence of a prolonged PR interval or first degree AV block doubled the risk of developing atrial fibrillation, tripled the risk of requiring an artificial pacemaker, and was associated with a small increase in mortality.