Signals from specialized heart tissue {sinoatrial node} {pacemaker} initiate and regulate heartbeat. Heart fibers beat by themselves. Blood carbon dioxide, blood thyroxin, blood epinephrine, vagus-nerve stimulation, body temperature, fever, and muscle stretching affect heart rate.
Signals go from sinoatrial node to specialized heart tissue {atrioventricular node} and then to ventricles.
4-Zoology-Organ-Circulation-Parts-Heart
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Date Modified: 2022.0225