Science Illustrated

Electrical wave flows through the heart

Our heartbeats are carefully coordinate­d by the body's own pacemaker. It sends rhythmic signals to the heart’s muscles, which cooperate to make sure that our bodies are supplied with oxygen-rich blood.


Biological pacemaker controls the heart 1

A small collection of cells known as the sinoatrial node is located in the wall of the heart’s right atrium, sending out electrical impulses at regular intervals. The impulses flow from there into the heart along special routes which ensure that the heart’s muscles contract in the right order.

Atria pump in step 2

First, the two atria contract. The right one includes oxygendepl­eted blood that has passed through the body, whereas the left atrium is full of oxygen-rich blood from the lungs. The atria force the blood on into the ventricles.

Valves ensure one-way ‘traffic’ 3

Cardiac valves located between atria and ventricles function as stop valves which make sure that the blood cannot flow back from ventricle to atrium.

Ventricles contract to despatch the blood 4

Contractio­n of the two ventricles is the last part of the heartbeat. The right ventricle full of oxygen-poor blood directs its contents towards the lungs, where the blood is oxidised. The left ventricle, where the muscles are stronger than those of the right, pumps oxygen-rich blood into the entire body via the aorta.

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