pacemaker

noun

• 1a person or animal who sets the pace at the beginning of a race, sometimes in order to help a runner break a record: he acted as a pacemaker for Bannister when he broke the four-minute mile
• a person who sets standards of achievement for others: unbeaten Rangers are the surprise pacemakers

• 2a device for stimulating the heart muscle and regulating its contractions.
• the part of the heart muscle (the sino-atrial node) which normally regulates contractions.
• the part of an organ or of the body which controls rhythmic physiological activity: the brain’s circadian pacemaker which regulates our ‘biological clock’