What are the events in the cardiac cycle?

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The cardiac cycle is the series of events that leads to blood being pumped to the lungs and around the body.

The cycle begins with the SAN (sino-atrial node). This is the hearts 'pacemaker'. It sends out a nerve impulse which spreads over the atria and causes them to contract (atria systole), forcing blood into the ventricals. The signal is not able to spread to the ventricals as a layer of non-connective tissue blocks the signal at the base of the atria.

The signal from the SAN is recieved at the AVN (atrio-ventricular node) at the top of the ventricals. This node sends a signal down the perkyne (or purkinje) fibres which travel in the insulating Bundle of His through the inter-ventrica septum to the base of the ventricles.

At the base of the ventricals (apex) a wave of contraction passes up the ventricals causing them to contract pushing blood up and out of the ventricals.

These events can be tracked on an ECG trace.

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