All patients will be screened prior to enrollment. Any patient with any commercially available pacemaker or ICD system implanted after 2001 who meet all of the inclusion criteria and none of the exclusion criteria, and who require a medically-indicated MRI as described above will be eligible to enroll in the study. The presence/absence of capped/abandoned/epicardial leads/subcutaneous coil will be confirmed and documented by review of the most recent chest x-ray obtained. The x-ray must post-date the most recent device/lead intervention, as determined by a review of the patient's medical record.