Case presentation : A 55-year-old female patient underwent implantation of a cardiac resynchronization therapy (CRT) defibrillator 6 years ago owing to nonischemic dilated cardiomyopathy. Her left-ventricular (LV) ejection fraction (EF) was 28% before implantation, her LV end-diastolic volume index (EDVI) was 144 mL/m2, and her LV end-systolic volume index (ESVI) was 104 mL/m2. Her intrinsic QRS complex was 155 ms with left bundle-branch block morphology. Despite being on optimal medication, she still experienced symptomatic heart failure (New York Heart Association class III). Now, 6 years later, she is doing very well (New York Heart Association class II). Her LVEF has increased to 38%, her EDVI has decreased to 95 mL/m2, and her ESVI has decreased to 59 mL/m2. Is this patient a superresponder to CRT? Were any of her baseline characteristics predictive for superresponse? What are the implications regarding her prognosis and clinical management? CRT is a cornerstone in contemporary heart failure management because of the reduction in morbidity and mortality after CRT implantation in patients who have the triad of: (1) symptomatic chronic heart failure (CHF), (2) a severely reduced LVEF (EF ≤ 35%), and (3) a wide QRS complex.1 The benefit to the individual patient, however, may vary widely. Although some demonstrate a good or even excellent response to CRT (referred to as superresponders), others show little to no effect.2 Indeed, evidence is accumulating that CRT may even induce harm in some individuals, especially in patients with a narrow QRS complex.3 What is the definition of nonresponse to CRT? Given the natural course of patients with CHF, stabilization of the disease indicates some response, whereas true nonresponders continue their downward course, and negative responders may even derive harm from CRT (Figure 1). The characteristics of superresponders to …