Heart attacks often come without warning, and although it's well documented that they're caused by atherosclerosis (plaque buildup on arterial walls), there are certain triggers that can set off a heart attack in people who are at risk. In a study published in The Lancet, Belgian researchers ranked various heart attack triggers according to their prevalence in people who are already at risk for cardiac problems. Here's a list of some of their more surprising findings, and some ways to protect yourself from heart attack triggers:

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