There are generally three parts to a pacemaker — a pulse generator, leads, and an electrode on each lead. As its name suggests, the pulse generator conducts electrical impulses to the heart via the lead, which touches the heart wall.
The pacemaker will not send electrical impulses unless the heart’s rate falls below the device’s programmed limit.
Advancements in technology have brought about the leadless pacemaker which does not require lead and, is instead, implanted directly into the heart using a catheter. This type of pacemaker can be used for single-chamber pacing; in patients with certain types of bradycardia.