Limited data regarding the effect of right ventricular pacing (RVP) on long-term survival following implantable cardioverter-defibrillator (ICD) implantation are available. The purpose of this study was to evaluate the effect of RVP on the long-term survival benefit of primary ICD therapy. Mortality data were obtained for all patients enrolled in the Multicenter Automatic Defibrillator Trial-II (MADIT-II) during an extended follow-up period of 8 years. The cumulative percent RVP during the trial was categorized as low (≤ 50% n = 369) and high (>50% n = 198). The benefit of ICD versus non-ICD therapy (n = 490) was evaluated in the two pacing categories during the early (0-3 years) and late (4-8 years) phases of the extended follow-up period. During the early phase of the extended follow-up period, ICD therapy was associated with similar benefits in the low-RVP and high-RVP subgroups (hazard ratio HR = 0.35 and 0.38, respectively, P <.001 for both). In contrast, during the late phase, the long-term survival benefit of the ICD was maintained among patients with low RVP (HR = 0.60, P <.001) and attenuated among those with the high RVP (HR = 0.89, P = .45). An increased risk for late mortality associated with high versus low RVP was evident only among patients without left bundle branch LBBB at enrollment (HR = 1.63, P = .002). Among ICD recipients, high RVP is associated with a significant increase in the risk of long-term mortality and with attenuated device efficacy. The deleterious effects of RVP are pronounced mainly in non-LBBB patients, suggesting a possible role for combined cardiac resynchronization-defibrillator therapy in this population.