There are two primary types of pacemakers: a standard pacemaker that triggers the chambers of the heart, and an internal defibrillator/pacemaker combination known as a cardioverter defibrillator.
The standard type of pacemaker sends an electrical impulse via special wires that are attached to the heart. This replaces the signal that is sent by the heart, which is faulty in patients who need a pacemaker.
A second type of pacemaker, the internal defibrillator/pacemaker combination, sends an electrical impulse to the heart to control the heart’s rate and rhythm, just as a standard pacemaker does. In addition to that function, it can also deliver a “shock” to stop a “lethal rhythm,” a heart rhythm that does not allow the heart to effectively function.
The idea of the shock is the same as the “shock with paddles” that you may have seen on television. However, because the device is attached to the heart with wires, the shock is much less powerful than what you may imagine.