Effects of a Single Oral Dose of KETone Ester ON Exercise Performance in Patients With Chronic Heart Failure

Inclusion Criteria: * Chronic Heart Failure NYHA II - III * LVEF ≤40% * Stable for the last 1 month prior to the study Exclusion Criteria: * Age \<18 years; * Unable or unwilling to undergo exercise MRI (physical disabilities, claustrophobia); * Unable to complete the exercise protocol during the screening visit according to the professional opinion of the investigators; * Comorbidities which can influence study results such as muscular dystrophies, peripheral artery disease, diabetes mellitus, severe anaemia (defined as Hb ≤6 mmol/L); * Pregnant/trying to get pregnant/breastfeeding during the period from the first exercise test until 4 weeks after the last exercise test); * Absolute contra-indications to undergo MRI according to the current UMCG protocols and guidelines (e.g. non-conditional medical device, recent device implantation, incompatible ferromagnetic objects in the body). * BMI \< 16 kg/m2; BMI \> 35 kg/m2 * Unable to understand study procedures; * Unable or unwilling to provide informed consent.