Electrical activity of the heart

The pumping activity of the heart is dependent on the electrical impulses generated by specialized fibers in the heart itself called the pacemaker or the SA node (sinoatrial node). The SA node is located in the wall of the right upper chamber of the heart called the right atrium. The muscle fibers of the heart are structurally different from muscle fibers in other parts of the body and are connected to each other in a special arrangement such that the impulses generated in that special spot in the right atrial wall are propagated and programmed to arrive at each of the other 3 heart chambers (left atrium, right ventricle and left ventricle) in perfect timing.




Electrical conduction pathway of the heart.
Original heart diagram illustrated by Patrick J. Lynch; illustrator; C. Carl Jaffe; MD; cardiologist Yale University Center for Advanced Instructional Media

The result is that the 2 atria receive electrical impulses at the same time and contract in unison, pushing blood out into the ventricles while the ventricles receive electrical impulses a bit later and are thus relaxed when the atria are contracting. By the time the ventricles finally begin to contract, the atria have emptied out, the building pressure in the ventricles cause the atrioventricular valves to close and blood is pushed out of both ventricles; from the right to the lungs and from the left to the aorta, the biggest artery in the body.

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