The heart's electrical system stimulates the contraction of the muscle cells of the four chambers, thereby causing blood to circulate through the chambers in a precise and sequential fashion. The stimulation begins in the sinus node, proceeds through the atria, then moves through the ventricles.

Source: Chung, M.K., and Rich, M.W. Introduction to the cardiovascular system. Alcohol Health and Research World 14(4):269–276, 1990.

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Prepared: February 2001