Can heat cause a high heart rate?

Heat related to the human body causes vein and artery dilation (expansion) and decreases pressure or blood flow (blood pressure). If a person has plaque severe enough that the body requires a certain pressure to push blood through it and you take that pressure away, the artery can spasm and close or be deprived of needed blood flow causing ischemia (lack of oxygen) or infarct (myocardial infarct or heart attack).