A pacemaker is a medical device which uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart.
The heart is a muscular organ in humans and other animals, which pumps blood through the blood vessels of the circulatory system.
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit.
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The primary purpose of a pacemaker is to maintain an adequate heart rate, either because the heart's natural pacemaker is not fast enough, or because there is a block in the heart's electrical conduction system.
Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute.
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Modern pacemakers are externally programmable and allow a cardiologist to select the optimum pacing modes for individual patients.
Some combine a pacemaker and defibrillator in a single implantable device.
Others have multiple electrodes stimulating differing positions within the heart to improve synchronisation of the lower chambers of the heart.