The heart has four chambers two at the top(atria) and two at the bottom (ventricles)the normal trigger for the heart to contract arises from the heart's natural pacemaker the SA node, which is in the top chamber.The SA node sends out regular electrical impulses causing the atrium to contract and pump blood into the ventricle.The electrical impulse then passes to the ventricles through a form called AV node(Atria-ventricular node).This electrical impulse spreads into the ventricles causing the muscle to contract and to pump blood to the lungs and the body.Chemicals which circulate in the blood and which are released by the nerves that regulate the heart,alter the speed of the pacemaker and the force of the pumping action of the ventricles.
hydah kerubo answered the question on May 1, 2018 at 18:09
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