Your heart: The basics
Your heart's electrical system
What makes your heart beat?
Your heart is controlled by electrical signals that tell its muscles when to contract and when to relax.
Each pulse begins in the right atrium at the sino-atrial (SA) node. The SA node functions like a pacemaker, controlling your sinus rhythm (your heart’s natural rhythm) and keeping your heart beating steadily and regularly.
Your heart’s electrical system
The electrical pulse passes from the SA node through the heart to another node called the atrioventricular (AV) node, and then on down into the ventricles, causing them to contract.
A normal pulse rate is 60 – 100 beats per minute. Of course, your heart will beat faster than that when you’re exercising or stressed and slower when you’re asleep.
The heart’s electrical activity can be measured and recorded using a machine called an electrocardiogram (an ECG or EKG – both abbreviations are commonly used).
Normal ECG
An ECG produces a “tracing”, like the one above, that shows how your heart is behaving, and this can be used to diagnose heart disorders.
To learn more about how the heart pumps blood around your body, take a look at How your heart pumps.
A single heartbeat: Electrical pulses and an ECG
To get an understanding of how the heart’s electrical system works it’s easiest to look at just one heartbeat.
The animation below shows how the electrical pulses flow from the SA node, which is up in the right atrium, down through the heart and all the way to the ventricles. In the inset box, we show the corresponding ECG tracing.
Your heart in a single beat
The ECG line is broken down into a series of points: P, Q, R, S, and T. Each point represents a phase of the electrical pulse and each phase produces a different physical reaction in the muscles of the heart.
Looking at our single heartbeat, this is what happens:
The P-wave causes the atria to contract and push blood down into the ventricles.
Then the Q-wave, R-wave, and S-wave, combined (the “QRS complex”), trigger the contraction of the ventricles, and this pushes blood out and around the body (from the left ventricle) and to the lungs (from the right ventricle).
Finally, the T-wave neutralizes the charge held in the cells and allows the muscles to relax, ready for the next heartbeat.
To learn more about how the heart pumps blood around your body, take a look at How your heart pumps.