- Sports One who sets the pace in a race. Also called pacer, pacesetter.
- A leader in a field: the fashion house that is the pacemaker. Also called pacesetter.
- 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.
- Any of several usually miniaturized and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle.
- Biochemistry A substance that regulates a series of related reactions.