British Heart Foundation
Normal heart rhythm (Sinus rhythm)
Every heartbeat is immediately preceded by a small electrical impulse which travels through the heart along a network of nerves called the Cardiac Conduction System.
Each electrical impulse starts high up in the Right Atrium in a region know as the Sinoatrial Node (SA Node). It then travels across the top two heart chambers (the Atria) causing them to contract simultaneously, before reaching the mid-point between the top and bottom chambers, a region known as the Atrioventricular Node (AV Node). Here, there is a short delay as the electrical impulse travels slower through the AV Node.
Once through, the electrical impulse travels fast along nerve fibres within the muscular walls of the ventricles causing them to contract simultaneously.
After a short recharge time, another electrical impulse starts following the same pathway.
A normal heart rate at rest (i.e. after sitting or lying down for 10-15mins) is typically between 60 – 100 beats per minute. If slower than this you have Bradycardia, something commonly seen in very active people. However even with top athletes it is abnormal to have a resting heart rate less than 40 beats per minute.
A heart rate above 100 beats per minute is described as Tachycardia.