This accessory adapts external cardiac defibrillation systems to enable safe defibrillation, pacing, and cardioversion inside the MRI bore with minimal effect on MR image quality. Commercially available external defibrillators are not designed to work in the MRI environment. An MR-compatible defibrillator is needed to safely perform cardiovascular MRI, in particular MR-guided interventional cardiovascular procedures, such as cardiac electrophysiology studies and cardiac catheterization. This accessory includes nonmagnetic defibrillator housing with MRI safety features, provides interface for MRI-compatible physiological monitoring, and optimizes defibrillator operation for the MRI environment. The accessory may include MRI-compatible modules for monitoring/recording electrocardiogram, blood pressure, pulse oximetry, and other physiological signals. It may also include a wireless transmitter and at least one module for electrical energy generation and/or stimulation.