Abstract: Neuromuscular electrical stimulation (NMES) is an option for increasing thigh muscle strength and endurance capacity in patients with chronic heart failure. Electromagnetic interference (EMI) by the signals with sensing of implantable cardioverter defibrillators (ICDs) is possible. The aim of the present pilot safety study was to test the safety of a long-term NMES in patients with ICDs. Six patients with subpectoral ICDs were subjected to long-term NMES of thigh muscles. Four inpatients received NMES to increase muscle strength, and two outpatients performed NMES as a home treatment to increase endurance capacity. During long-term NMES, all patients together received 14 139 799 biphasic electrical pulses and 412 425 on-phases without adverse events. ICD function after the stimulation period revealed no abnormalities in any patient. These results indicate that long-term NMES of thigh muscles seems to be safe in patients with ICDs, providing that an individual risk is excluded before.