From HomoExcelsior

1. pacesetter 2. pacesetter 3. A part of the body, such as the mass of muscle fibers of the sinoatrial node, that sets the pace or rhythm of physiological activity. 4. Any of several usually miniaturized and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle. 5. A substance that regulates a series of related reactions.

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