A single-chamber pacemaker uses one lead, placed either in the right atrium or the right ventricle of your heart. (Most single-chamber pacemakers have a lead attached to the right ventricle.)
When Attached in the Atrium- Leads attached in the right atrium are designed to correct abnormalities in the heart's sinoatrial (SA) node (a condition known as "sick sinus syndrome" ). This kind of atrial pacing corrects the slow or irregular heart rates that are common with this condition. A pacemaker lead attached in the atrium will ensure that your heart's atrium will contract at an exact millisecond so blood will be pumped into the ventricle.
When Attached in the Ventricle - Leads attached in the right ventricle correct a slow or unsteady heartbeat that results from a condition called "heart block," in which the heart's necessary electrical currents are blocked from reaching the atrioventricular (AV) node. A pacemaker lead attached in the ventricle will ensure that your heart's ventricles contract rhythmically and fully, to increase the amount of blood that your heart can pump into your lungs and body.