Pacemakers basically take over the rhythm of the heart if it goes too slow. They are designed to pace the heart when the heart cannot go fast enough to provide adequate synchronized heart rate function. There are most often 2 electrical wire leads placed in the heart. One in the upper back chamber or atrium and 1 in the right ventricle or lower pumping chamber. Pacing leads are electrical wire devices that are placed down in the chambers of the heart.  These wires are screwed into the heart  On one end and the wires are screwed into the pacing Box on the other end. The pacing Box is then placed in the left upper chest right by the clavicle.  Common companies who make these pacemakers are Medtronic, Boston scientific and Abbott laboratories.