Heart attacks, strokes, and cardiac arrests seem like they come out of the blue, but most don't. They usually appear after cholesterol-rich plaque has festered in the arteries that nourish the heart and brain. So what makes one happen at a particular time? A trigger, reports the July 2007 issue of the Harvard Heart Letter.
Waking from sleep. Before you wake up, your body trickles stress hormones into the bloodstream. This helps you get up, but also slightly stresses the heart. That, along with dehydration that occurs overnight and the overnight fade in protection from heart medicines, may explain why heart attacks are most common in the morning.
Heavy physical exertion. Shoveling snow, running, and other strenuous activities can be triggers. But don't be afraid to exercise—exertion is much less likely to cause trouble in people who exercise regularly.
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