An implantable device that contains a power source, a device for producing electrical signals, and a conductor assembly for communicating the electrical signals to biological matter. The conductor assembly contains of a conductor that is capable of being flexed at least about 15 degrees and that has a resistivity at 20 degrees Centigrade of from about 1 to about 100 micro ohm-centimeters. The conductor assembly also contains a magnetic shield located above the flexible conductor; the magnetic shield contains an antithrombogenic composition. The magnetic shield also contains a magnetic shielding material that has a magnetic shielding factor of at least about 0.5.