The heart’s electrical system:
A healthy heart beats steadily and rhythmically at a rate of about 60 to 100 beats per minute when at rest (normal sinus rhythm). During strenuous exercise, the heart can increase the amount of blood it pumps up to four times the amount it pumps at rest within only a matter of seconds.
When heart cells in the upper heart chambers (atria) receive an electrical signal, they contract (pump) and then relax. The blood from the atria is pumped into the relaxed lower heart chambers (ventricles) and then the ventricles pump blood to the body.
In a healthy heart, each heart beat begins in the sinus node (the heart’s natural pacemaker), which is located in the right atrium. The electrical signal from the sinus node (sinoatrial or SA node) starts an electrical chain reaction that spreads across both atria, much like ripples on the calm surface of a pond. This causes the atria to contract and pump blood into the ventricles.
This electrical chain reaction continues from the atria through an area between the atria and ventricles called the atrioventricular node (AV node or AV junction). The AV node connects to conduction pathways that relay the signal to the ventricles. The AV node acts as an electrical gateway to the ventricles. The conduction pathways deliver the signals to the ventricles and the ventricles pump blood to the body.
An irregularity in the heart’s electrical system is called an arrhythmia, or heart rhythm disorder. Rhythm disorders can cause the heart to beat too slowly (bradycardia) or too fast (tachyarrhythmia).