The technology behind pacemakers (PMs) and implantable cardioverter defibrillators (ICDs) is constantly evolving with specific features which render devices ever more sophisticated. Although shielding and manufacturing features have rendered them more immune to electromagnetic interference (EMI), there remains safety concerns with high risk exposure. Based on the International Standards Organization standard 14117, PMs and ICDs on the market should offer resistance to 5.4 kV/m (for 60 Hz electric fields). This value is above the ICNIRP international recommendation for public exposure (4.2 kV/m). The goal of this study was to expose PMs and ICDs to electric fields up to 20 kV/m, to determine the el445ectric field threshold for EMI. Such high electric field levels can be encountered in industrial settings (power utility substations) and in the right of way of high voltage (735 kV) power lines (theoretically up to about 9 kV/m at midspan). Forty device models currently on the market (21 PMs and 19 ICDs, including CRTD) from 5 manufacturers were tested in vitro in a high voltage laboratory to 20 kV/m. Devices were mounted in a saline tank at human torso height. Devices were set up both as left and right sided pectoral implants. When programmed to nominal parameters, in bipolar mode, all PMs were immune to EMI up to 8.6 kV/m (8.6 kV/m for least resistant to > 20 kV/m for most resistant). When programmed to higher sensitivity levels or in unipolar mode, the EMI threshold decreased to as low as 1.5 kV/m in some devices. When programmed to nominal parameters, all ICDs were immune to EMI up to 2.9 kV/m (2.9 kV/m for least resistant to > 20 kV/m for more resistant). In many cases, a slight decrease in sensitivity level conferred much greater resistance to EMI. There was no significant difference in EMI threshold field values for left compared to right sided implants. EMI remains a concern when PMs and ICDs are exposed to electric fields. These results reconfirm the need for individualized decisions for the safety of employees with PMs and ICDs in their work environment. For general public safety, no significant concern should arise in individuals with PMs programmed to nominal settings, in bipolar mode. For the minority of patients with devices in unipolar mode or with very sensitive settings, appropriate counselling should be given at implantation or at medical follow up, for example avoiding to remain under high voltage power lines (> 230 kV).