The heart is triggered to beat by electrical impulses from the brain. If there is an interruption to this signal, the heart may cease to beat completely, with obvious consequences. More commonly, though, a patient will suffer from a condition that causes an irregular heartbeat, or arrhythmia.
 

We have classified arrhythmias within the acquired disease category, because this is thought to be the most common form. However, dogs with congenital heart disease or no underlying heart disease may also suffer from arrhythmias.
 

There are different types of arrhythmias, some of which are breed specific (see below).

In this illustration, the heart is beating irregularly as a result of an interruption to the impulses sent by the brain.
 

In some cases, the heart may simply cease to beat. In most cases, though, the heart will beat less effectively than it should, thereby reducing the volume of blood pumped around the body.

All breeds may suffer from different types of arrhythmia, but the following are known to be at higher risk: Cavalier King Charles, Pugs, Miniature Schnauzers, Boxers, German Shepherds, Dobermanns and Irish Wolfhounds.