A pacemaker is a device that helps regulate the the rhythm of the heart as well as the rate at which it beats. It may be used temporarily, such as after open heart surgery, or placed permanently, with a minimally invasive procedure.
A normal heart beats at a steady pace, but there are many conditions that can make the heart beat irregularly. The rate may be too fast or too slow, or the heart may no longer beat in the normal "lub-dub" fashion. If the heart is not beating properly, a pacemaker can be used to regulate the rhythm.
A pacemaker sends an electrical impulse to the muscle of the heart telling it when to beat. If one of the chambers of the heart is working improperly, the pacemaker can be attached there, or to multiple chambers if necessary.
Conditions that can be treated with a pacemaker include atrial fibrillation and bradycardia (slow heart rate). In some cases, the pacemaker can help insure the left and right atrium or ventricles contract at the same time. There is also a defibrillator/pacemaker combination available, which is used to treat abnormal tachycardia (an irregular and overly fast heart rate).