Source:http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19566.jpg

The Pacemaker is a device to provide electrical stimulus to the heart muscles when the normal stimulus from the SA node is not adequate or interrupted. The picture shows the leads from the pacemaker travelling to various locations in different chambers of the heart. This is a permanent implant and hence the biomaterials used in this device have to be very stable over the entire life of the patient. These biomaterials may vary from metals, to polymers that come directly in contact with the in-vivo environment.