As promised a brief and basic explanation of the cardiac cycle/heartbeat. Apologies if you know this already.
The heart is a muscular pump with 4 chambers; 2 at the top (atria- right and left) and 2 at the bottom (ventricles-right and left).
Electrical impulses, which occur naturally, pass through these chambers in turn from top to bottom and this results in the collection and ejection of blood from the heart around the body.
Blood comes into the atria, they help to pass blood into the ventricles, the ventricles squeeze blood out again.
This stimulation from the natural electrical impulse happens repeatedly at regular intervals but always atria first followed by the ventricles second. Each time this happens it produces one cardiac cycle/heart beat
The electrical activity which passes through the heart, during this process, is picked up on the surface of the skin by electrodes and this produces the different parts of the ECG.
See part 2 for ECG components....