Inclusion Criteria:  ICD in situ Clinical indication for VT ablation; incessant VT or receiving appropriate ICD therapies for VT despite anti-arrhythmic drugs Ischaemic or non-ischaemic heart disease  Exclusion Criteria:  Valvular heart disease precluding LV access Cardiotomy within previous 3 months Acute coronary syndrome within 6 weeks Dialysis patients Coagulopathy/Thrombocytopaenia Pregnancy/breastfeeding women CMR contraindicated Prognosis <12 months Unable to provide informed consent