pace·mak·er (pāsˈmāˌkər)

1. A part of the body, such as the specialized mass of cardiac muscle fibers of the sinoatrial node, that sets the pace or rhythm of physiological activity.
2. Any of several usually miniaturized and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle.
3. A substance whose rate or reaction sets the pace for a series of chain reactions.
4. The rate-limiting reaction itself.

Related Forms:

• paceˈmakˌing adjective & n.

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pacemaker

fixed-rate artificial pacemaker