The heart displays autorhythmicity i.e. it will continue to beat under appropriate conditions even when removed from the body in the absence of extrinsic nerves. However in an intact heart, there is highly synchronised contraction of the heart muscle which is initiated by electrical activity. The heart behaves like a pump due to the contraction of the atria first, followed by the ventricles during each heart beat.

The mechanism of action can be understood more easily as two separate events:

• the Cadiac Cycle
• the Excitation of the Heart

Despite having put them as two events, they take place during the same time. Therefore don't mistake these events taking place one after the other but they work together.

After the Phases of the Cardiac Cycle there a link of a video at the bottom of the page to help visual the cycle better.