Contemporary heart failure (HF) guidelines recommend insertion of a primary prevention implantable defibrillator (ICD) in patients with left ventricular ejection fraction less than 35% (LVEF < 35%) on maximally tolerated medical therapy. Nevertheless, there are a substantial number of HF patients who have LVEF>35% and hence do not qualify for ICD, who succumb to sudden cardiac death (SCD). At present our tools to reliably risk stratify these patients with mild-moderate systolic dysfunction (LVEF 36-50%) are poor. It is likely that these patients have ventricular scar and/or replacement fibrosis as a substrate for their malignant arrhythmia. Cardiovascular magnetic resonance imaging (CMR) can reliably identify and quantify both ventricular scar (seen in Ischaemic cardiomyopathy, ICM) and replacement myocardial fibrosis (seen in Non-Ischemic Cardiomyopathy, NICM).