Millions of patients have had their lives saved or their quality of life significantly improved by implantable cardiac pacemakers. A technology emerging as an indispensable clinical diagnostic tool is magnetic resonance imaging (MRI). However, the MRI electromagnetic fields can cause malfunction of pacemakers, adversely affective patients. Pacemakers can also generate magnetic fields that distort the MR images. Because of these adverse effects, patients with pacemakers cannot undergo diagnostic testing with MRI. We have demonstrated that pacing can be safely performed during MR imaging, without distortion of images, as long as the pacemaker itself and the pacemaker input are appropriately protected against electromagnetic interference. We have also demonstrated that conducting cases can be built which do not distort the image, do not cause heating, and do not have forces applied to them by the magnetic field. This project is devoted to developing a prototype MRI-compatible pacemaker that can be implanted and tested in an animal model. The design principles validated in Phase I will be used during Phase II to build clinical prototypes for generating data with which to obtain an Investigational Device Exemption (IDE) from the Food and Drug Administration to start clinical testing of this technology. PROPOSED COMMERCIAL APPLICATION: When MRI-compatible pacemakers become available, they will replace all of the non-compatible pacemakers in future implantations. A future market for MRI-compatible pacemakers may exceed $2B per year.