Background Implantable cardioverter-defibrillators (ICDs) are generally considered a contraindication to magnetic resonance imaging (MRI). Objective The purpose of the ProMRI Phase C study, a multicenter, prospective, single-arm, nonrandomized study, was to evaluate the clinical safety of the Biotronik ProMRI Iforia ICD system during MRI. Methods Patients were enrolled after ICD implantation, with either a dual-chamber DR-T or single-lead VR-T DX system. Study-defined, nondiagnostic cardiac or thoracic spine MRI was performed at least 1 week after enrollment. ICDs were placed into MRI mode with ventricular fibrillation (VF) detection/therapy programmed "off" before scan and restored to non-MRI mode after scan. Interrogation was performed before, immediately after, and 1 month post-MRI. The primary end-points were (1) ventricular pacing threshold increase >0.5 V from pre-MRI to 1 month post-MRI; (2) R-wave amplitude decrease >50% from pre-MRI to 1 month post-MRI or R-wave amplitude <5 mV at 1 month post-MRI; and (3) MRI and ICD system-related serious adverse device effects. Results One hundred seventy patients were enrolled at 39 US centers. One hundred fifty-three patients underwent MRI (25.7% cardiac, 74.3% thoracic spine) and completed follow-up. Freedom from the primary end-points was met in all but 1 subject, in whom reduced R-wave amplitude was detected 1 month post-MRI. No serious adverse device effects occurred during the course of the study. Conclusion These results demonstrate the clinical safety and efficacy of the ProMRI ICD system in patients subjected to thoracic spine and cardiac MRI imaging in 1.5-T scanners.