Pronunciation: (pās'mā"kur), [key]
2. Med.an electronic device implanted beneath the skin for providing a normal heartbeat by electrical stimulation of the heart muscle, used in certain heart conditions.
3. Anat., Physiol.any specialized tissue that governs a rhythmic or cyclic biological activity, as the sinoatrial node of the heart that controls heartbeat.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.