Background: Cardiac resynchronization therapy (CRT) is effective in reducing morbidity and mortality in systolic heart failure patients with cardiac dyssynchrony as demonstrated in studies with primarily Western populations. Although CRT devices with a defibrillator (CRT-D) became available in Japan since 2006, their efficacy remains uncertain in Japanese patients. In this prospective, multicenter study, the efficacy of CRT-D therapy in an all-Japanese population was compared with the study conducted in the US, Multicenter InSync ICD Randomized Clinical Evaluation (MIRACLE-ICD). Methods and Results: Ninety-three patients were evaluated according to the subject selection criteria of the MIRACLE-ICD study, and 80 patients were enrolled. Results at baseline and 6-month post-CRT-D implantation were compared in terms of composite clinical response (CCR) and other secondary endpoints. Quality of life (QOL) was assessed with a validated Japanese version of the Minnesota Living with Heart Failure questionnaire. CCR was improved in 55 patients (68.8%), unchanged in 14 (17.5%), and worsened in 11 patients (13.7%) (MIRACLE-ICD general phase: 62.0%, 13.4% and 24.6%, respectively). Non-inferiority was verified by 1-sided test with 10% equivalence margin. QOL score improved significantly (50.0±26.2 vs. 23.6±20.2, P<0.01). Conclusions: The MOMIJI study demonstrated that CRT-D effectiveness as assessed with CCR was non-inferior to the trials conducted outside Japan, thus suggesting that the benefits of CRT-D are similar between Japanese and non-Japanese patients.  (Circ J 2012; 76: 1911–1919)