Abstract Background Implantable cardioverter defibrillator (ICD) is recommended for patients with non-ischaemic heart failure (HF) and left ventricular ejection fraction (LVEF) ≤35%, although most patients will not experience any appropriate ICD intervention. We assessed if cardiovascular magnetic resonance (CMR) findings may predict benefit from ICD implantation. Methods and results We retrieved the data of all patients (n=183) with non-ischaemic HF receiving an ICD for primary prevention at our Institution, and undergoing CMR within 1 month before implantation. 183 patients were evaluated (men 73%, median age 66 years, LVEF 24%, N-terminal fraction of pro-B-type natriuretic peptide 1217 ng/L, atrial fibrillation, flutter or atrial ectopic rhythm 21%). They received single-chamber (n=21, 12%), dual-chamber (n=34, 19%), or cardiac resynchronization therapy devices (n=127, 69%); 1 patient (1%) received a subcutaneous defibrillator. Twenty patients (11%) experienced a shock for ventricular tachycardia or fibrillation (VT/VF) over 2.5 years (0.8–5.4), and 13 (7%) had an inappropriate shock over 2.7 years (0.9–5.4). Late gadolinium enhancement (LGE) was present in 146 patients (80%), but on average accounted for limited percentage of LV mass (4% [2–11%]). LGE mass independently predicted shocks for VT/VF (HR 2.13, 95% CI 1.02–4.47; p=0.045). LGE mass ≥14% (the best cut-off at receiver operating characteristics analysis) independently predicted shocks for VT/VF (HR 3.82, 95% CI 1.51–9.68; p=0.005). LGE mass <4% was the only univariate predictor of inappropriate shocks (HR 4.82, 95% CI 1.07–21.76; p=0.041). Conclusions Patients with non-ischaemic HF and LGE mass ≥14% benefit most from ICD, while those with LGE mass <4% display mainly inappropriate shocks.