Inclusion Criteria for Patients with Cardiovascular Disease:  Aged 40-years and older. Eligible for cardiac rehabilitation following a cardiac-related hospital admission, coronary artery disease (including angina, myocardial infarction, percutaneous coronary intervention, or coronary artery bypass graft surgery).  Inclusion Criteria for Healthy controls:  Aged 40-years and older. Never been diagnosed with cardiovascular disease or coronary artery disease. No history of cardiovascular disease risk factors including hypertension, hyperlipidemia, diabetes, obesity (body mass index > 30) or smoking. Current body mass index < 30kg/m2  Exclusion Criteria for all participants:  Known cerebrovascular or neurological disease Known moderate-severe respiratory disease, pregnancy, Orthopedic limitations affecting exercise capability Unable to read and speak English Unable to complete study-related activities Contraindications to hypercapnia Contraindications to maximal exercise testing MRI incompatible devices Unwillingness to undergo MRI scan (e.g. due to anxiety or claustrophobia).