This is used to ensure that the heart beats at a fast enough rate.  It comprises a small box (‘Generator’) placed under the skin, connected to one, two or three wires (‘leads’) which pass through the vein behind the collarbone into the heart.  The pacemaker may have a single lead into either the top (‘right atrium’) or bottom (‘right ventricle’) chamber of the heart, or a lead in both.  A special type of pacemaker, called a ‘biventricular pacemaker’ (also known as Cardiac Resynchronisation Therapy, or CRT) has three leads and is used for patients whose heart does not necessarily go too slow, but is weakened and inefficient.  It is performed under local anaesthetic, and is done through a small incision (about 3cm, or 1-1 ½ inches) just below the collarbone usually on the side opposite to the hand the patient uses to write.  Recovery is usually quite quick, but the patient is usually asked to limit how much they use the arm on the same side of the body as the pacemaker for the first month (hence it is usually put on the opposite side to the arm the patient uses most!).  There is a small risk of complications, such as bleeding, infection, puncturing the lung behind the vein (behind the collarbone), and one of the leads displacing.  The risk of any of these is usually no more than 1 in 100.  The patient will need to have the pacemaker checked regularly.  This is done by simply putting a header (which looks a little like a computer ‘mouse’) over the skin above the pacemaker.  The header is connected to a programmer which retrieves information about how the heart has been behaving since the last check.  Changes can also be made to the settings of the pacemaker in this way.  Patients are usually seen one month after the procedure, and then every six to twelve months after that.