A study put out by the American Heart Association looked at 200,000 heart attack deaths. It tracked temperatures and pollution on case days. Investigators found an 18 percent higher risk during two-day heat waves when the mercury was between 82 and 97 degrees. It climbed to a 74 percent higher risk during four-day heat waves when the temps climbed between 94 and 109 degrees. Most concerning, the risk doubled when the hottest days were coupled with high pollution.