It is routinely recommended that patients with pacemakers, implantable cardioverter defibrillators (ICD), and cardiac resynchronization therapy-defibrillators (CRT-D) avoid bioelectrical impedance analysis (BIA)--a commonly used method to estimate body composition--because of the concern for the potential for BIA interference with pacemaker or ICD function. However, the prevalence of such interference is not known. Assess for incidence of interference between BIA and ICD or CRT-D devices. Twenty patients with heart failure and cardiac implanted electronic devices (50% ICD, 50% CRT-D) underwent BIA during real-time device interrogation to detect interference. Study patients were 90% male, with mean age 54 ± 14 years, and mean LVEF 23 ± 11%. Devices from all four leading cardiac device manufacturers were included. Device therapies were temporarily disabled to prevent inappropriate shocks. During body composition testing using BIA, no evidence of interference with ICD function was seen in any patient, including no telemetry disruption, no oversensing on any lead, and no patient symptoms. Despite the manufacturers' recommendation to avoid BIA in patients with ICDs, this study showed no evidence of any interference in 20 patients. Bioimpedance analysis might be safe in such patients, but further confirmatory studies are required.