Heat extremes are associated with greater risk for cardiovascular death. The pathophysiologic mechanisms mediating this association are unknown. The objective of this study is to quantify the myocardial blood flow (MBF) requirements of heat exposure. After conductin this experimental sutudy it can conclude that heat exposure that increases core temperature by 1.5 °C nearly doubles MBF. Changes in MBF did not differ by age or presence of CAD, but some older adults with CAD may experience asymptomatic myocardial ischemia.