A cardiac impulse is a cardiac excitation that travels in a wavelike motion and initiates the cardiac cycle. The cardiac cycle refers to the rhythmic beating of the heart.
Specialized cells throughout the heart are the origins of the cardiac impulses. The pacemaker initiates the cardiac action. The conducting system then distributes the impulses throughout the heart.
A cardiac impulse starts at the sinoatrial node that is located where the superior vena cava meets the right atrium. From the sinoatrial node, a cardiac impulse travels to the atrioventricular node. The atrioventricular node is located in the lower septal wall of the right atrium. From the atrioventricular node, a cardiac impulse runs along the bundle of His. At this point, the cardiac impulse enters the junction that lies between the two atria and two ventricles. From there, a cardiac impulse branches down either side of the ventricular septum. These branches continue to divide into what is known as the Purkinje network that is found in the endocardial layer of the ventricles. Here, the branches stimulate muscle cells to contract.