Odds are, you or someone you love will have a heart attack, also known as a myocardial infraction or MI. Heart attacks occur about every 35 seconds in the United States, and most occur in the morning, a time when the platelets in the blood are especially "sticky" and prone to form clots. "Many people are awakened by a heart attack at four in the morning," says Sharonne Hayes, MD, director of the Mayo Clinic's Women's Heart Clinic. At least one study, however, has found that morning isn't a prime time for heart attacks among people who regularly take aspirin, which helps keep platelets from sticking together.

Even though someone in the U.S. dies from a heart attack every three and a half minutes, this is one medical event the majority of doctors and emergency medical technicians are trained to respond to. Care tends to be swift and efficient, if a little rote. "When I had my heart attack, the doctors at the hospital practically yawned—they had seen so many cases like mine," laughs Rene Delgado, 52, of New York City, who had a heart attack in 2006. "They knew exactly what to do, and because the care I got was so well-organized and precise I lost no heart muscle. If you must have a life-threatening medical emergency, a heart attack isn't the worst one to have."

While treatments for heart attacks are more effective than ever, half of all deaths still occur within one hour after a heart attack. That means getting to a hospital should be priority one if you or someone else experiences the first symptoms of a heart attack. How well you respond—and how fast—is a matter of life and death.