The OLEA-HF study aims to explore whether daily supplementation of extra-virgin olive oil (EVOO) for 12 weeks during participation in a cardiac rehabilitation program (standard of care) is feasible in patients with heart failure with reduced ejection fraction (HFrEF). The investigators will also determine the effects of EVOO on functional capacity and quality of life.

Inclusion Criteria:

• Diagnosed with HFrEF with left ventricular ejection fraction ≤35 %.
• Referred to and enrolled in the standard cardiac rehabilitation program at Sentara Cardiac Rehabilitation Center, but has not yet initiated/started cardiac rehabilitation (i.e., has not attended the first cardiac rehab session).
• Able and willing to comply with study procedures and provide informed consent.

Exclusion Criteria:

• Co-morbidity expected to limit survival (e.g., terminal illness).
• End-stage renal disease.
• Unstable fluid overload.
• Current pregnancy (self-disclose).
• Habitual use of EVOO greater than 4 tablespoons per day.
• Known allergy or sensitivity to olive oil or its components.
• Unwillingness or inability to incorporate EVOO or dietary recommendations.