BACKGROUND Heart failure with recovered ejection fraction (EF) is a recently described clinical entity. There is insufficient information on the management of implantable-cardioverter defibrillator (ICD) patients with improved EF at generator replacement. METHODS AND RESULTS We examined the incidence of appropriate shocks in 91 consecutive patients with ICDs for primary prevention of sudden death who underwent generator replacement. Improved EF was defined as both EF >35% at generator replacement and increase in EF by ≥10% since original implantation. Patients were 70 ± 11 years old, and 76% had ischemic cardiomyopathy. At generator replacement, 25 patients (27%) had improved EF (0.49 ± 0.08 vs 0.31 ± 0.07 at baseline; P < .0001). Over 6.2 ± 2.2 years of follow-up after original implantation, 9 patients (36%) with improved EF versus 19 (29%) with unchanged EF had appropriate ICD shocks (P = .51). Incidence of appropriate ICD shocks was similar between the two groups before (P = .90) and after (P = .97) generator replacement. Of the 9 improved EF patients with appropriate shock, 4 had shocks before generator replacement, 2 had shocks before and after generator replacement, and 3 patients, who never had shocks before, had their first shock after generator replacement. CONCLUSIONS Some ICD patients whose EF improves to >35% at generator replacement remain at risk for appropriate ICD shocks.