The purpose of this study is to determine the increase in myocardial blood flow during heat exposure and how this response is affected by age and coronary artery disease.

As a result of climate change, heat waves are more frequent and of longer duration. These heat waves are associated with a higher risk of hospitalization and mortality in vulnerable populations such as people with cardiovascular disease or cardiovascular risk factors. It has been hypothesized that this observation may be explained by the cardiovascular demands imposed by heat exposure.

Heat exposure requires increased cardiac work that may place individuals with cardiovascular disease at risk of ischemic events if the metabolic demand is not compensated by adequate blood supply. However, the extent to which cardiac work increases during heat exposure remains unknown. The aim of this study is to test the hypothesis that heat exposure increases myocardial blood flow and that this increase is affected by age and coronary artery disease.

Inclusion Criteria for Healthy Participants:

• Age between 18-40 years or 60-80 years
• Non-smoker (≥1 year)
• Non-diabetic
• Normal kidney function
• Body Mass Index <30 kg/m2
• Resting blood pressure <140/<90 mmHg
• Resting heart rate <100 bpm

Inclusion Criteria for Participants with Coronary Artery Disease:

• Age between 60-80 years old
• History of angiographic coronary disease (≥70% arterial diameter narrowing of at least one major epicardial coronary artery) and/or prior coronary revascularization and/or documented prior acute coronary syndrome and/or perfusion defect during stress testing
• Stable medications (≥4 weeks) prior to enrollment

Exclusion Criteria for Healthy Participants:

• Diagnosis of heart, vascular, respiratory, neurological or metabolic disease and/or a prescription of medication for the treatment of these diseases
• Pregnancy or lactation
• Dyslipidemia not controlled by medication

Exclusion Criteria for Participants with Coronary Artery Disease:

• Recent hospitalization (<3 months) related to coronary artery disease
• Unstable angina (<3 months)
• Recent coronary artery bypass surgery (<3 months)
• Left branch block
• Ejection fraction <40% and/or clinical signs of heart failure
• Severe valvular heart disease
• Hypertension not controlled by medication
• Diabetes not controlled by medication and/or serious complications related to diabetes