“Heart block is a problem with your heartbeat signal moving from the upper to lower part of your heart. The signal can only get through sometimes, or not at all. This makes your heart beat slowly or skip beats. People with second-degree or third-degree heart block may experience fainting, tiredness and shortness of breath.

Heart block is an issue with a heartbeat signal traveling from the top chambers of your heart to the bottom chambers of your heart. Normally, electrical signals (impulses) travel from your heart’s upper chambers (atria) to your lower chambers (ventricles). The signal moves through your AV node, a cluster of cells that link the electrical activity from your top to bottom chambers. If you have heart block, the signal only makes it to your ventricles some of the time, if at all.

The result is a heart that may not work well. Your heart may beat slowly or skip beats. In severe cases, heart block can affect your heart’s ability to pump blood, causing low blood flow to your entire body.

Other names for heart block are atrioventricular (AV) block or a conduction disorder.  The heart block is between the upper chambers (atriums) and the lower chamber (ventricles) with the electrical activity responsible to make your heart beat properly.”

Cleveland Clinc (Heart Block: Types, Symptoms & Causes)