The heart is a muscle that contains a special electrical system that can produce and send electrical impulses. Known as the conduction system, it is a complex network of cells and fibers through which electrical impulses travel, triggering a heartbeat.

In a normal heart, the electrical pulses that travel through the heart begin in the sinoatrial node (sinus node) at the top of the right side of the heart. From here, they move down through the atria, causing the upper chambers to contract.

As the pulses continue to travel down, they are diverted into the two lower chambers of the heart (ventricles) by the bundle of His (pronounced "hiss"). The impulses then cause the ventricles to contract, completing a full beat of the heart. this regular cycle repeats itself, pumping blood effectively out of the heart.

If rhythms are interrupted, delayed or sent down the wrong path, the heartbeat may become irregular or abnormally fast or slow (arrhythmia).