WordNet
n. a specialized bit of heart tissue that controls the heartbeat [syn: pacemaker, sinoatrial node, SA node]
Wikipedia
right|thumb|350px|Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.
The contraction of cardiac muscle ( heart muscle) in all animals is initiated by electrical impulses known as action potentials. The rate at which these impulses fire controls the rate of cardiac contraction, that is, the heart rate. The cells that create these rhythmic impulses, setting the pace for blood pumping, are called pacemaker cells, and they directly control the heart rate. They make up the cardiac pacemaker, that is, the natural pacemaker of the heart. In most humans, the concentration of pacemaker cells in the sinoatrial (SA) node is the natural pacemaker, and the resultant rhythm is a sinus rhythm.
Sometimes an ectopic pacemaker sets the pace, if the SA node is damaged or if the electrical conduction system of the heart has problems. Cardiac arrhythmias can cause heart block, in which the contractions lose any useful rhythm. In humans, and occasionally in animals, a mechanical device called an artificial pacemaker (or simply "pacemaker") may be used after damage to the body's intrinsic conduction system to produce these impulses synthetically.
Usage examples of "cardiac pacemaker".
True, close study of her bosom might reveal the inequality which betrayed her use of a cardiac pacemaker, but nowadays many people wore such accessories by the time they were seventy or even younger.
The subtlety and sense of timing of a thermostat or a cardiac pacemaker, Pete decided -- that's what it takes to be a hunter -- a feeling for the rhythm of things and a power over them.