A pacemaker is a device that allows the heart to maintain a regular, continuous beat. The heart is equipped with a natural pacemaker that produces electrical signals, stimulating the heart muscle to beat at specific intervals. This natural pacemaker, or sinoatrial node (sy-no-AY-tree-all NODE), is located at the top of the heart's right upper chamber, or atrium (AY-tree-um). It's made up of a group of cells capable of sending out electrical impulses approximately 60 to 100 times per minute. The electrical signals pass through the heart on a specific path, stimulating both sides of the heart muscle to contract or beat at precise times. There are several conditions, however, in which this node doesn't perform it's job properly. It may develop an arrhythmia, causing the heart to beat too quickly or too slowly or with an irregular rhythm. Or, another part of the heart may begin producing electrical signals on its own, interfering with the proper impulse frequency sent out by the sinoatrial node and stimulating an arrhythmia. Further, the node's signals may not be effectively transmitted from the heart's upper atrial chambers to the lower ventricular (ven-TRIK-you-lar) chambers. This is known as heart block, since the signals are partially or completely prevented from traveling on their specified route through the heart. Depending on the severity of these various situations, an artificial pacemaker may be used to take over the sinoatrial node's functions. An artificial pacemaker can be either permanently implanted or external and temporary. Usually, it consists of a tiny, battery-powered device that emits electrical impulses. These are sent by wire to an electrode attached to the heart. Often, the mechanism is designed to sense the heart's slowing down or speeding up, responding as needed to keep a specific, steady beat. When using an artificial pacemaker, it's generally important to be aware of nearby appliances, cellular phones, and medical equipment that may interfere with the pacemaker's ability to produce a steady signal. If you're concerned about your heart's function, or have questions about pacemakers, contact a healthcare provider.