A pacemaker includes an electrode line having a lead and an electrode. The electrode includes a carbon nanotube composite structure having a matrix and a carbon nanotube structure located in the matrix. The matrix comprises a first surface and a second surface substantially perpendicular to the first surface. The carbon nanotube structure includes a first end electrically connect to the lead. The carbon nanotube structure is substantially parallel to the second surface of the matrix. A distance between the carbon nanotube structure and the second surface of the matrix is less than 10 micrometers.