The Cardiac Cyle

... The Cardiac Cyle The Cardiac cycle is activated by an electrical stimulus called the cardiac impulse. This stems from a small mass of tissue found in a region of the right atrium, called the Sino atrial node or pacemaker. The electrical stimulus generated by the Sino-atrial node spreads out into the walls of the atria causing their contraction, in other words atrial systole. A band of fibrous tissue splits the atria from the ventricles, and stops the impulse passing straight on to the ventricles. Here the Atrio-ventricular Node picks up the impulse. From here, it is conducted through the band of fibrous tissue, along a short bundle of specialised conducting fibres called the Bundle of His. The bundle separates within the septum that divides the two ventricles, into left and right branches, which conducts the impulse to the tip of the heart, where the branches turn up along the ventricular myocardium

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