MEDICAL DICTIONARY
Rate, heart: Number of heart beats per minute. The normal resting adult heart beats regularly at an average rate of 60 times per minute. (Young children's hearts beat faster). The speed of the heartbeat (heart rate) is governed by the speed of electrical signals from the pacemaker of the heart, the SA node, located in the right atrium (upper chamber of the heart). The electrical signals from the SA node travel across the atria and cause these two upper heart chambers to contract, delivering blood into the lower heart chambers, the ventricles. The electrical signals then pass through the AV node to reach the ventricles. Electrical signals reaching the ventricles cause these chambers to contract, pumping blood to the rest of the body, generating the pulse. During rest, the speed of electrical signals originating from the SA node is slow, so the heart beats slowly. During exercise or excitement, the speed of signals from the SA node increases, and the heartbeat quickens.
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