A new study found almost half of all heart attacks cause no obvious symptoms, yet they can still be life-threatening.
The research followed more than 9,000 middle-aged men and women for almost 13 years. It's one of the biggest studies to examine so-called silent heart attacks, and to explore them across racial and gender groups.
Researchers at Wake Forest University's medical school led the government-funded study. Results were published online in the American Heart Association's journal, Circulation.
